Quiz: Mechanical Engineering 7 Aug 2020

Quiz: Mechanical Engineering
Exam: ISRO (TECHNICAL ASST.)
Topic: Miscellaneous

Each question carries 4 mark.
Negative marking: 1 mark
Time: 15 Minute

Q1. The pressure head loss experienced by fluid flow due to friction in a pipe increases with
(a) increasing length of pipe
(b) increasing diameter of pipe
(c) decreasing length of pipe
(d) both b and c

Q2. Which of the following statements is correct for a body in simple harmonic motion?
1. Acceleration is proportional to displacement from mean position
2. Velocity is minimum at mean position
3. Acceleration is maximum at mean position
(a) 1 and 2
(b) 2 and 3
(c) only 1
(d) only 2

Q3. The amount of heat flow in unit time by conduction
(a) Decreases with increase in area of the body
(b) Increases with increase in area of the body
(c) Increases with increase in thickness of body
(d) Decreases with increase in temperature difference between the faces of the body

Q4. If an unconstrained steel bar is heated uniformly then which of the following is correct for it?
(a) Thermal stress will be developed in it.
(b) Tensile stress will be developed in it.
(c) Compressive stress will be developed in it.
(d) No stress will be developed in it.

Q5. A rotating ceiling fan completes 800 revolutions per minute. If the tip of the blade is at a radius of 0.5 m, then the blade tip speed is (take π=22/7)
(a) 42 m/s
(b) 22 m/s
(c) 66 m/s
(d) 88 m/s

Q6. Which of the following statements are correct when related to thermodynamic system?
1. Enthalpy is a property
2. Enthalpy is path independent function
3. Enthalpy is path dependent function
(a) Only 1
(b) 1 & 2
(c) 1 & 3
(d) 2 & 3

Q7. The number of Nitrogen atoms in 56 grams of Nitrogen gas is
(a) 6.023 ×10^23
(b) 12.023 ×10^23
(c) 24.092 ×10^23
(d) 6.023 ×10^27

Q8. If feed per revolution is 2 mm and lathe spindle is rotating with 600 rpm then find out the time taken to machine 400 mm length workpiece
(a) 0.33 sec
(b) 20 sec
(c) 2 min
(d) 1.33 sec

Q9. Which of the following milling processes is also called climb up milling?
(a) Up-milling
(b) Down-milling
(c) Face-milling
(d) End-milling

Q10. Which of the following thread is used for bench vices?
(a) Acme
(b) Square
(c) Buttress
(d) Trapezoidal

Solutions

S1. Ans (a)
Sol. We know that pressure head loss in a pipe is given by Darcy-Weisbach’s equation.
h=(fLV^2)/(d.2g)
Here, h increases with decreasing diameter and increasing length of the pipe.

S2. Ans (c)
Sol. In simple harmonic motion, acceleration of a particle is proportional to the displacement from the mean position.
i.e. Acceleration ∝-(Displacement)
Acceleration is minimum at the mean position and maximum at the end positions.

S3. Ans (b)
Sol. We know that Fourier’s law of conduction for heat flow rate is given by
Q=-kA.dT/dx
Q increases with increasing area and temperature difference and Q decreases with increasing thickness of the wall along the heat flow.

S4. Ans (d)
Sol. Stress is defined as internal resistance invoked by a body to the external forces. If there is no external force on the body then there is no stress in it. Hence, in an unconstrained steel bar, there is no stress due to heating.

S5. Ans (a)
Sol. Blade tip speed for a rotor is given by
V=rω …………(1)
Given,
N= 800 rpm then ω=2πN/60=(2×22×800)/(60×7)
From equation (1)
V=0.5×(2×22×800)/(60×7)
V=41.9 or 42 m/s

S6. Ans (b)
Sol. Enthalpy is a property of a thermodynamic system. So, it is path-independent function.

S7. Ans (c)
Sol. According to Avogadro’s Law,
1 mole (or 28 grams) of Nitrogen gas contains 6.023 ×10^23 molecules, so, 56 grams of Nitrogen gas contains 12.046×10^23 molecules.
1 molecule (or 28 grams) of Nitrogen gas has 2 mole-atoms, hence 56 grams (or 2 molecules) of Nitrogen gas has four mole-atoms or 24.092 ×10^23 atoms.

S8. Ans.(b)
Sol.Given,
N=600 rpm
L=400 mm
Feed per rev= 2 mm
Time taken to machine the component=L/fN=400/2X600
=0.33 minute or 20 sec

S9. Ans (a)
Sol. Up-milling is a milling process in which cutter moves in the opposite direction of work-piece motion. It is also called conventional milling process because of its cutter motion opposite to the work-piece.

S10. Ans (c)
Sol. The buttress thread form, also known as the breech-lock thread form, refers to two different thread profiles. Buttress threads are used for one side motion transmission only i.e. in bench vices etc.

Quiz: Mechanical Engineering 06 Aug 2020

Quiz: Mechanical Engineering
Exam: UPPSC AE
Topic: Miscellaneous

Each question carries 3 mark.
Negative marking: 1 mark
Time: 10 Minute

Q1. Which one of the following is the desirable section for torsional loading conditions?
(a) angle Section
(b) Channel Section
(c) I-section
(d) Box-type section

Q2. If the load at the free end of a uniform cantilever beam is increased, then failure will occur
(a) at the middle
(b) at the fixed end
(c) at the point of application of load
(d) anywhere in the span

Q3. Which of the following term is used for Proof resilience per unit volume of a material?
(a) resilience
(b) modulus of elasticity
(c) modulus of resilience
(d) toughness

Q4. Mushroom follower is also known by another name that is
(a) flat faced follower
(b) Spherical faced follower
(c) Roller follower
(d) Knife edge follower

Q5. A governor is said to be stable if
(a) Radius of rotation of ball decreases as the equilibrium speed decreases
(b) Radius of rotation of balls increases as the equilibrium speed decreases
(c) Radius of rotation of balls increases as the equilibrium speed increases
(d) Radius of rotation of balls decreases as the equilibrium speed increases

Q6. Which of the following is correct for Axode?
(a) Locus of Instantaneous axis
(b) Axis parallel to Instantaneous axis
(c) Axis perpendicular to Instantaneous axis
(d) Instantaneous axis

Q7. Which of the following mechanism work behind when the auto rickshaw takes a turn?
(a) It has a differential mechanism
(b) The tyres slip during turns
(c) Power is transmitted to only one of the wheels
(d) None of these

Q8. Which of the following statement is correct for critical damping?
(a) It provides basis of determining critical damping.
(b) It predicts nature of vibration
(c) It provides a measure of the relative amount of damping in a system.
(d) It enables measurement of damping.

Q9. How the shock absorbing capacity of a bolt can be increased?
(a) Tightening it properly
(b) Increasing shank diameter
(c) Grinding the shank
(d) Using washer

Q10. The pressure head loss experienced by fluid flow due to friction in a pipe reduces with
(a) increasing length of pipe
(b) increasing diameter of pipe
(c) decreasing length of pipe
(d) both b and c

Solutions

S1. Ans.(d)
Sol. When torsion is dominant then Box-type section used & second most probable section for torsion dominant is I Section because the shear center of these section not lies outside.

S2. Ans.(b)
Sol. If the load at the free end of a cantilever beam is increased the failure will occur at the fixed end because due to increase of load moment resisted by fixed support is increased and when support moment reaction increased beyond its limit then failure occur.

S3. Ans.(C)
Sol. Proof resilience is defined as the maximum energy that can be absorbed up to the elastic limit, without creating a permanent distortion. The modulus of resilience is defined as the maximum energy that can be absorbed per unit volume without creating a permanent distortion.

S4. Ans.(a)
Sol. Flat faced follower is also known as mushroom follower
Types of followers –
1. Knife edge follower
2. Roller follower
3. Flat faced or mushroom follower
4. Spherical follower

S5. Ans.(c)
Sol. If each speed of governor possesses a particular radius of governor, then it is called stable governor.

S6. Ans.(a)
Sol. The instantaneous center changes every moment, its locus is called centrode and the surface generated by the instantaneous axis is called the axode.

S7. Ans.(b)
Sol. Rickshaws takes sharp turn by using the concept of slip. When one of the wheels will slip against the road, rickshaw turns.
We cannot use a differential mechanism in it because wheels and axis are rigidly connected to each other.

S8. Ans.(b)
Sol. for critical damping (ς=1)
It is used to predicts the nature of vibration.

S9. Ans.(c)
Sol. There are following ways to increase shock absorbing capacity of a bolt.
Shock absorbing capacity or strain energy (U)
∪ ∝ l(length of bolt)
∪ ∝ 1/A
Or
∪ ∝ 1/d^2
Hence, L↑→∪↑
d↑→∪↓

S10. Ans (d)
Sol. We know that pressure head loss in a pipe is given by Darcy-Weisbach’s equation.
h=(fLV^2)/(d.2g)
Here, h decreases with increasing diameter and decreasing length of the pipe.

Quiz: Mechanical Engineering 31 July 2020

Quiz: Mechanical Engineering
Exam: ISRO (TECHNICAL ASST.)
Topic: Miscellaneous

Each question carries 4 mark.
Negative marking: 1 mark
Time: 15 Minute

Q1. Annealing of steel takes place at a temperature
(a) Just above the lower critical temperature
(b) Just below the lower critical temperature
(c) Just above the upper critical temperature
(d) Just below the upper critical temperature

Q2. Weber number is the ratio of
(a) Square root of ratio of inertia force to surface tension force
(b) Square root of ratio of inertia force to viscous force
(c) Square root of ratio of inertia force to gravity force
(d) None of these

Q3. Kelvin-Plank statement is a corollary of
(a) First law of thermodynamics
(b) Second law of thermodynamics
(c) Zeroth law of thermodynamics
(d) Third law of thermodynamics

Q4. Diffuser is of converging cross section at outlet for
(a) Supersonic flow
(b) Sonic flow
(c) Subsonic flow
(d) None of the above

Q5. If the center distance between the involute gears is increased then which of the following will be the effects of it?
1. Pitch circle diameter is increased.
2. Pressure angle is decreased.
3. Velocity ratio is increased.
4. Pressure angle is increased.
(a) Only 1
(b) 1 and 3
(c) 1 and 4
(d) 2 and 3

Q6. Which of the following factors contributes in increase of material removal rate in electro chemical machining?
(a) Increase in valency of metal ion
(b) Increase in density of metal
(c) Increase in voltage between workpiece and tool
(d) None of these

Q7. The locus of point on a circle which rolls without slipping along a straight line is known as
(a) An involute
(b) A cycloid
(c) A parabola
(d) An ellipse

Q8. If for a turning job, the length of the work is 400 mm and the taper is 1:20, the set-over required for the tail stock to achieve the taper is
(a) 15 mm
(b) 20 mm
(c) 4 mm
(d) 5 mm

Q9. A solid metal brick weighs 90 N in air and 50 N, when submerged in water then what is the weight of the water displaced by body?
(a) 30 N
(b) 60 N
(c) 40 N
(d) 50 N

Q10. If a boat covers a 50 km in 10 min when it is running downstream and covers the same distance in 20 min when running upstream then find out the speed of flowing river water
(a) 37
(b) 41.6
(c) 20.8
(d) 16

Solutions

S1. Ans (b)
Sol. This process is mainly suited for low-carbon steel. The material is heated up to a temperature just below the lower critical temperature of steel.

S2. Ans (a)
Sol. Weber Number is a dimensionless characteristic number used to analyse fluid flows where there is an interface between two different fluids. As a dimensionless quantity, it describes as the square root of the ratio between the inertial forces and the surface tension forces for liquids flowing through a fluid medium.

S3. Ans (b)
Sol. The Kelvin–Planck statement of the second law of thermodynamics states that it is impossible to devise a cyclically operating heat engine, the effect of which is to absorb energy in the form of heat from a single thermal reservoir and to deliver an equivalent amount of work.

S4. Ans (a)
Sol.
1. If Mach Number (Ma<1) then flow is subsonic.
Nozzle is converging and diffuser is diverging at outlet.
2. If Mach Number (Ma>1) then flow is supersonic.
Nozzle is diverging and diffuser is converging at outlet.

S5. Ans (c)
Sol. For the involute gear profile increase in the center to center distance leads to increase in pressure angle so the pitch circle radius of the gears gets changed and it is increased. But velocity ratio between gears will remain constant.

S6. Ans (c)
Sol. We know that
Volume MRR in ECM = (A.V)/(F.ρ.R.v)
Here,
A = Atomic weight of metal ion of workpiece
V = Voltage between work-piece and tool
F = Faraday’s constant
ρ = Density of metal
R = Resistance between workpiece and tool
v = Valency of metal ion

S7. Ans (b)
Sol. A cycloid is the curve traced by a point on a circle as it rolls along a straight line without slipping.

S8. Ans.(b)
Sol. Set-over or offset required on tail-stock for taper turning=taper X length of workpiece
Set-over or offset length= 1/20 X 400=20 mm

S9. Ans.(c)
Sol. We know,
Weight of the water displaced=Buoyancy on body= (weight of body in air – weight of body in water)
=90-50
=40 N

S10. Ans.(c)
Sol.
Let speed of river is v and speed of boat in still river is u and total distance covered either side is 50 km.
Given,
For Downstream flow-
(50×1000)/(u+v)=10×60

u+v = 83.33……….(1)

For up-stream flow-
(50×1000)/(u-v)=20×60

u-v = 41.66………..(2)

Solving equation (1) and (2)..

Speed of river (v) = 20.83 m/s

Quiz: Mechanical Engineering 30 July 2020

Quiz: Mechanical Engineering
Exam: UPPSC AE
Topic: Miscellaneous

Each question carries 3 mark.
Negative marking: 1 mark
Time: 10 Minute

Q1. The stress strain curve for cast iron during tensile test would exhibit
(a) A straight line
(b) A parabola
(c) A sudden break
(d) None of these

Q2. Gradually increasing temperature of flue gases at inlet to chimney for given steam output is an indication of
(a) Higher effectiveness of boiler
(b) Fouling of heat transfer surfaces
(c) Raising of steam temperature
(d) High calorific value of coal being burnt

Q3. Which of the following is true for martensite?
(a) It is a supersaturated solution of carbon in alpha iron
(b) It is a supersaturated solution of carbon beta iron
(c) It is a supersaturated solution of carbon gamma iron
(d) It is a supersaturated solution of carbon delta iron

Q4. The crystal structure of Titanium (Ti) at room temperature is
(a) Body-Centered Cubic (BCC)
(b) Face-Centered Cubic (FCC)
(c) Hexagonal Close-Packed (HCP)
(d) Simple Cubic (SC)

Q5. Which of the following purpose is served by the chills?
(a) Mixed in sand to enhance its collapsibility
(b) Metallic objects to provide very high heat extraction capability of sand mould
(c) Metallic objects to provide strength of sand mould
(d) Metallic objects to provide very low heat extraction capability of sand mould

Q6. Oxidizing flame is used for the welding of:
(a) Brass
(b) Mild steel
(c) Cast steel
(d) None of these

Q7. Which of the following is an application of merchant circle?
1. Improve the quality of a product
2. Find the principal stress and principal strain
3. Establish the shear angle relationship in machining
(a) only 1
(b) 1 and 2
(c) 1 and 3
(d) only 3

Q8. Which of the following is also known as three-dimensional cutting system?
(a) Oblique cutting
(b) Orthogonal cutting
(c) Both oblique and orthogonal cutting
(d) None of these

Q9. When we need to make the same parts again and again on a processing machine then which of the following machine is used?
(a) Center lathe
(b) Tool-room lathe
(c) Special purpose lathe
(d) Capstan lathe

Q10. For an ideal reflector, the energy distribution at higher temperature is largely in the range of
(a) Longer wavelength
(b) Shorter wavelength
(c) Remains same at all wavelengths
(d) No relation of wavelength with temperature

Solutions

S1. Ans.(c)
Sol. The stress -strain curve for cast iron during tensile test would exhibit a sudden break due to brittle failure.

S2. Ans (b)
Sol. If the temperature of flue gases increases from inlet to chimney outlet then it is a sign of fouling of heat transfer surfaces.

S3. Ans.(a)
Sol. A meta-stable phase of steel formed by transformation of austenite below a temperature 240℃ is known as martensite. It is an interstitial solid solution of carbon in α-iron.

S4. Ans.(c)
Sol. Titanium has hexagonal closed packed structure at room temperature. Generally, pure titanium can crystallize in two crystal structures: α titanium and β titanium. When it crystallizes at low temperatures (room temperature), the hexagonal close-packed (HCP) structure of alpha titanium is formed.

S5. Ans.(b)
Sol. There are certain areas in the casting that needs high heat extraction of heat due to variation in geometry of casting. For this purpose, we use chills that provide critical cooling rate.

S6. Ans.(a)
Sol. A slightly oxidizing flame is used in torch brazing of steel and cast iron. A stronger oxidizing flame is used in the welding of brass or bronze.

S7. Ans.(d)
Sol. According to Merchant circle relationship,
2ϕ+β-α=π/2
Or
ϕ=π/4+α/2-β/2
Here, ϕ is shear angle, α is rake angle and β is friction angle.

S8. Ans.(a)
Sol. When the cutting edge of the tool is inclined or making an angle (other than 90°) with the direction of feed, then it is called oblique cutting. This cutting is also called three-dimensional cutting because of force components in all three directions.

S9. Ans.(d)
Sol. A capstan machine is a processing machine used to make the same parts again and again. The cutting bits are mounted on a rotatable turret known as a capstan, which permits the client to rapidly change the introduction of the bits for slicing without needing to take off the first bit and afterward mount the second.

S10. Ans (b)
Sol. For an ideal reflector, the energy distribution at higher temperature is largely in the range of shorter wavelength.

Quiz: Mechanical Engineering 28 July 2020

Quiz: Mechanical Engineering
Exam: ISRO (TECHNICAL ASST.)
Topic: Miscellaneous

Each question carries 4 mark.
Negative marking: 1 mark
Time: 15 Minute

Q1. Higher critical temperature of steel is
(a) 950℃
(b) 1560℃
(c) 800℃
(d) 723℃

Q2. Which of the following represents Reynolds number?
(a) Ratio of thermal conductivity to kinematic viscosity
(b) Ratio of inertia force to viscous force
(c) Ratio of heat convected to heat conducted
(d) None of these

Q3. If degree of superheat is increased in vapour compression refrigeration cycle then
(a) Refrigeration effect decreases
(b) Refrigeration effect increases
(c) Work input of compressor decreases
(d) None of these

Q4. When the Mach number is more than unity, then the flow is
(a) Supersonic
(b) Sonic
(c) Subsonic
(d) None of the above

Q5. The moment of inertia of a circular section of diameter D about its polar axis is________the moment of inertia about its diameter.
(a) four times
(b) double
(c) three times
(d) half

Q6. Which of the following type of tool is used in the ultrasonic machining process?
(a) Glass
(b) Cast iron
(c) Brass
(d) Diamond

Q7. Which of the following can be used to reduce interference between two involute gears?
(a) Increase width of the gear teeth
(b) Increase center distance between gears
(c) Decrease pressure angle
(d) None of these

Q8. The heat that must be absorbed by ice of mass 1 kg at -5℃ to take it to water at 10℃ is (specific heat of ice is 2.1 kJ/kg-K, specific heat of the water is 4.2 kJ/kg-K and latent heat of fusion of ice is 310kJ/kg)
(a) 363 kJ
(b) 243 kJ
(c) 192 kJ
(d) 203 kJ

Q9. There are five numbers 3, 4, 5, 7 and 8. The average value and root mean square value of these numbers are
(a) 13, 5
(b) 13.5, 5.7
(c) 5.7, 13.5
(d) 4, 5

Q10. Which of the following is valid condition for maximum power transmission in a belt?
(a) Total tension is equal to centrifugal tension
(b) Total tension is 2π times centrifugal tension
(c) Total tension is thrice the centrifugal tension
(d) Total tension is half the centrifugal tension

Solutions

S1. Ans (a)
Sol. Higher critical temperature of steel is 925℃ and lower critical temperature of steel is 723℃.

S2. Ans (b)
Sol. Reynolds Number(Re)=(Inertia Force)/(Viscous Force)=ρVd/μ
Here,
ρ=Density of fluid
V=Average velocity of fluid
d=Diameter of conduit
μ=Dynamic viscosity of fluid

S3. Ans (b)
Sol. As degree of superheat is increased in vapour compression refrigeration cycle then refrigeration effect and work input to compressor both increases.

S4. Ans (a)
Sol.
1. If Mach Number (Ma<1) then flow is subsonic.
2. If Mach Number (Ma=1) then flow is sonic.
3. If Mach Number (Ma>1) then flow is supersonic.
4. If Mach Number (Ma>3) then flow is hypersonic.

S5. Ans (b)
Sol.
Moment of inertia about the diameter=(πD^4)/64
Moment of inertia about polar axis=(πD^4)/32

S6. Ans (c)
Sol. For ultrasonic machining, we use tool of ductile material which can embed brittle abrasive slurry within itself.

S7. Ans (b)
Sol. There are following ways to reduce interference between gears.
1. Use of larger pressure angle
2. Increase in center distance
3. Tooth stubbing
4. Increasing number of teeth on gears keeping diameter same

S8. Ans (a)
Sol. Heat absorbed by ice at -5℃ to convert into water 10℃ = heat taken by ice from -5℃ to 0℃ + heat taken for phase change of ice into water at 0℃ + heat taken by water from 0℃ to 10℃
=1×2.1×(0-(-5)+1×310+1×4.2×(10-0)
=362.5 kJ

S9. Ans (b)
Sol.
Average value=(Sum of elements)/(Total number of elements)=(3+4+5+7+8)/5=13.5
Root mean square value=√((3^2+4^2+5^2+7^2+8^2)/5)=5.7

S10. Ans (c)
Sol.
For maximum power transmission in a belt,
Total tension in the belt (T) = 3 × Centrifugal Tension (Tc)

Quiz: Mechanical Engineering 27 July 2020

Quiz: Mechanical Engineering
Exam: UPSSSC JE
Topic: Miscellaneous

Each question carries 1 mark
Negative marking: 1/4 mark
Time: 10 Minutes

Q1. Which of the following is another name of reversible adiabatic process?
(a) Isothermal process
(b) Isochoric process
(c) Isentropic process
(d) none of these

Q2. Which of the following is correct for Hart mechanism?
(a) It consists of eight links
(b) It consists of six links
(c) It consists of four links
(d) It consists of twelve links

Q3. Which of the following type of loads acts on a rotating shaft carrying a unidirectional
transverse load?
(a) Variable bending stress
(b) Variable shear stress
(c) Constant bending stress
(d) Constant shear stress

Q4. Which of the following represents the compositions of photo-chemical smog?
(a) NOX and HC
(b) CO and CO2
(c) Excess O2
(d) Soot and PM

Q5. When a ship enters the Ganga river from Bay of Bengal, Which of the following things
will occur?
(a) Ship will rise a little
(b) Ship will fall a little
(c) It remains at same level
(d) It depends upon boat density

Q6. To accomplish which of the following needs, surge tank is used?
(a) To reduce frictional loss in pipe
(b) To ensure uniform flow in pipe
(c) To relieve the pressure due to water hammer
(d) To reduce cavitation

Q7. For what type of columns Euler’s formula is valid?
(a) Short column
(b) Both short and long column
(c) Weak column
(d) Long column

Q8. What type of gears we use, if the velocity reduction ratio is above 100?
(a) Spur gear
(b) Worm and worm gear
(c) Helical gear
(d) Bevel gear

Q9. The effects of work transfer from a high-pressure body to a low-pressure body are:
1. The energy is conserved
2. The entropy is not conserved
3. The availability is not conserved
Which of the above statements are correct?
(a) 1 and 2 only
(b) 1 and 3 only
(c) 2 and 3 only
(d) 1, 2 and 3

Q10. Which of the following devices is used to heat feed-water by utilizing the heat of the exhaust flue gases before leaving through the chimney?
(a) Superheater
(b) Economizer
(c) Air preheater
(d) ID fan

Solutions

S1. Ans (c)
Sol. A Reversible Adiabatic Process is also known as Isentropic Process. It is an idealized thermodynamic process which is adiabatic and in which the work transfers of the system are frictionless; there is no transfer of heat or of matter and the process is reversible.

S2. Ans.(b)
Sol. Hart mechanism consists of six links.

S3. Ans.(a)
Sol. Some fibre is subjected to tensile and compressive bending tress.

S4. Ans (a)
Sol. Photo-chemical smog is produced when pollutants from the combustion of fossil fuels react with sunlight. The energy in the sunlight converts the pollutants into other toxic chemicals. In order for photo-chemical smog to form, there must be other pollutants in the air, specifically nitrous oxides and other volatile organic compounds (VOCs).

S5. Ans (b)
Sol. Due to density of sea water is more than that of river water, hence more volume of boat has to be sunk in the river water than that in sea water.so floor level will fall of boat in river water.

S6. Ans.(c)
Sol. Surge tank is an open reservoir provided in between penstock to
(i) absorb the pressure wave due to sudden blockage of flow in the turbine which will reduce water pressured hammer problem
(ii) to serve for emergency supply and to maintain constant head at inlet of turbine

S7. Ans.(d)
Sol. As long column fails in buckling only, Euler formula also derived at the same assumption.

S8. (b)
Sol. For high velocity reduction ratio (more than 50), we use worm and worm wheel gear drive.

S9. Ans.(d)
Sol. When there is a decrease in pressure (High to low), then there is always an entropy
generation and loss of availability according to second law of thermodynamics. But energy
is always conserved according to first law of thermodynamics

S10. Ans.(b)
Sol. Economizer is situated before air pre-heater in the flue gas path.

Quiz: Mechanical Engineering 24 July 2020

Quiz: Mechanical Engineering
Exam: ISRO (TECHNICAL ASST.)
Topic: Miscellaneous

Each question carries 4 mark.
Negative marking: 1 mark
Time: 15 Minute

Q1. An isolated system is one in thermodynamics in which there is
(a) energy and mass transfer
(b) no energy and mass transfer
(c) energy transfer but no mass transfer
(d) no energy transfer but mass transfer

Q2. A heat pump for domestic heating operates between a cold system at 0°C and the hot
system at 6°C. What is the minimum electric power consumption if the heat rejected is 40000 kJ/hr?
(a) 2 kW
(b) 3 kW
(c) 4 kW
(d) 5 kW

Q3. Vertical component of pressure force on a submerged curved surface is
(a) equal to the force on a vertical projection of the curved surface
(b) equal to horizontal force component
(c) equal to the product of pressure at centroid and surface area
(d) equal to the gravity force of liquid vertically above the curved surface up to free surface

Q4. Which of the following is the effect of large clearance volume in reciprocating compressor?
(a) increased volume flow rate
(b) reduced volume flow rate
(c) lower suction pressure
(d) lower discharge pressure

Q5. Which of the following is a method to achieve maximum heat dissipation through a fin? (a) It should have maximum lateral surface at the root side of the fin
(b) it should have maximum lateral surface towards the tip side of the fin
(c) It should have maximum lateral surface near the centre of the fin
(d) It should have minimum lateral surface near the centre of the fin

Q6. Which of the following is used for the cooling of piston of an I.C. engine?
(a) Water
(b) Air
(c) Fuel oil
(d) Lubricating oil

Q7. Which of the following is the effect of changing center distance between gears in involute gear system?
(a) Pressure angle changes
(b) Velocity ratio changes
(c) Pitch circle remain unaffected
(d) Law of gearing does not satisfy

Q8. Which of the following type of bolt is preferred for service conditions involving jarring, vibration and pulsation of the working load?
(a) long bolt with increased elasticity
(b) short bolt with high rigidity
(c) bolt with castle nut
(d) bolt with a dished washer

Q9. Which of the following is also the second name of line imperfection?
(a) Miller defect
(b) Frenkel defect
(c) Schottky defect
(d) Edge dislocation

Q10. On which of the following place on a cutting tool, flank wear occurs?
(a) Relief face of the tool
(b) Rake face
(c) Cutting edge
(d) Nose of the tool

Solutions

S1. Ans (b)
Sol. There are three types of thermodynamic systems:
Open system: Both mass and energy transfer take place
Closed system: Only energy transfer takes place
Isolated system: No mass and energy transfer take place.

S2. Ans (a)
Sol. Given data
T2=0°C=273 K
T1=60°C
=(60+273)K=333K
Q1=80000 kJ/hr=40000/3600 kJ/s
= 11.11 kW
COP =T1/(T1-T2 )=333/(333-273)=5.55
Also, COP =Q1/W
∴5.55=11.11/W
or,W=11.11/5.55 = 2 kW

S3. Ans (d)
Sol. Vertical component of pressure force on the submerged curved surface is equal to the gravity force of liquid vertically above the curved surface up to the free surface.

S4. Ans (b)
Sol. The clearance volume is the space between piston top of inner surface of the cylinder head. The clearance volume reduces the capacity of the compressor and volume flow rate.

S5. Ans (a)
Sol. By having maximum lateral surface at the root side of the fin, we can get maximum heat dissipation through a fin.

S6. Ans (d)
Sol. Piston of diesel engine are usually cooled by lubricating oil. In addition, the lubricant on the cylinder walls must function as a seal to minimize the amount of gases of combustion that pass the piston rings and enter the crankcase.

S7. Ans (a)
Sol. The common tangent to the base circle changes when the distance between centre of two gears changes. So, the angle between the common tangent to base circle or action line with common tangent to pitch circle changes or pressure angel changes.

S8. Ans (c)
Sol. The castle nut consists of a hexagonal portion with a cylindrical upper part which is slotted in the line with the centre of each face. The split pin passes through two slots in the nut and a hole in the bolt, so that a positive lock is obtained unless the pin shears. It is extensively used in jobs subjected to sudden shocks and considerable vibration such as in automobile industry.

S9. Ans (d)
Sol. Edge dislocation is also known as line defect. Frankel and Schottky defect are both point defects.

S10. Ans (a)
Sol. Flank wear mainly occurs at the side relief face of the cutting tool due to friction between the workpiece surface and cutting tool face.

Quiz: Mechanical Engineering 23 July 2020

Quiz: Mechanical Engineering
Exam: UPPSC AE
Topic: Miscellaneous

Each question carries 3 mark.
Negative marking: 1 mark
Time: 10 Minute

Q1. Match List-I (Process) with List-II (characteristic) and select the correct answer using the codes given below the lists:
List-I
A. Throttling process
B. Isentropic process
C. Free expansion
D. Isothermal process
List-II
1. No work done
2. No change in entropy
3. Constant internal energy
4. Constant enthalpy
Codes:
A B C D
(a) 4 2 1 3
(b) 1 2 4 3
(c) 4 3 1 2
(d) 1 3 4 2

Q2. An inventor says that his new concept of an engine, while working between temperature limits of 27°C and 327°C rejects 45% of heat absorbed from the source. His engine is then equivalent to which one of the following engines?
(a) Carnot engine
(b) Diesel engine
(c) An impossible engine
(d) Ericsson engine

Q3. An oil of specific gravity 0.9 has viscosity of 0.28 stokes at 38°C. What will be its viscosity in Ns/m²?
(a) 0.2520
(b) 0.0311
(c) 0.0252
(d) 0.0206

Q4. Consider the following statements:
The increase in metacentric height
1.Increases stability
2.Decreases stability
3.Increases comfort for passengers in a ship
4.Decreases comfort for passengers in a ship
Which of the above statements are correct?
(a) 1 and 3
(b) 1 and 4
(c) 2 and 3
(d) 2 and 4

Q5. In a steam nozzle, to increase the velocity of steam above sonic velocity by expanding steam below critical pressure
(a) A vacuum pump is added
(b) Ring diffusers are used
(c) Divergent portion of the nozzle is necessary
(d) Abrupt change in cross-section is needed

Q6. For quick response of a thermocouple to observe varying temperature of fluids
(a) wire diameter must be large
(b) wire material density must be large
(c) wire material specific heat must be large
(d) wire surface heat transfer coefficients must be large

Q7. Consider the following statements for multi-jet carburettor:
1.Acceleration jet is located just behind the throttle valve.
2.Idle jet is located close to the choke.
3.Main jet alone supplies petrol at normal engine speed.
Which of these statements are correct?
(a) 1, 2 and 3
(b) 1 and 2
(c) 2 and 3
(d) 1 and 3

Q8. Which one of the following statements is not correct?
(a) Hooke’s joint is used to connect two rotating co-planar, non-intersecting shafts
(b) Hooke’s join is used to connect two rotating co-planar intersecting shafts
(c) Oldham’s coupling is used to connect two parallel rotating shafts
(d) Hooke’s joint is used in the steering mechanism for automobiles.

Q9. Two shafts A and B are of same material, and A is twice the diameter of B. The torque that can be transmitted by A is
(a) 2 times that of B
(b) 8 times that of B
(c) 4 times that of B
(d) 6 times that of B

Q10. High energy rate forming process used for forming components from thin metal sheets or deform thin tubes is
(a) Petro-forming
(b) Magnetic pulse forming
(c) Explosive forming
(d) Electro-hydraulic forming

Solutions

S1. Ans (a)
Sol. Throttling process: Enthalpy is constant (to measure the quality of steam)
Isentropic process: Entropy is constant.
Free expansion: No work done
Isothermal process: Constant internal energy.

S2. Ans (c)
Sol.
Carnot efficiency of engine,
η=1-T2/T1 =1-300/600=0.5
But according to the inventor’s claim
Efficiency of engine = 1–0.45=0.55
∵ Efficiency of actual engine cannot be greater than Carnot efficiency. So, this is an
impossible engine.

S3. Ans (c)
Sol. Dynamic viscosity,
μ=ρυ=(0.9×1000)×(0.28×10^(-4))
=0.0252 Ns/m²

S4. Ans (b)
Sol. The increase in metacentric height increases stability but decreases comfort for passengers due to increases in frequency of oscillations.

S5. Ans (c)
Sol. For supersonic flow conditions, nozzle is divergent and diffuser is convergent in design.

S6. Ans (d)
Sol. If surface that transfer coefficient is large then the rate of heat transfer will be more and hence thermocouple will be quick to respond to varying temperature of fluids.

S7. Ans (d)
Sol. Idle jet is located close to butterfly valve (Throttle)

S8. Ans.(a)
Sol. Hooke’s joint: This joint is used to connect two non-parallel, intersecting shafts. It also used for shafts with angular misalignment where flexible coupling does not serve the purpose. Thus, Hooke’s joint is a mean of connecting two rotating shafts whose axes lie is one plane, their directions making a small angle with each other.

S9. Ans.(b)
Sol. Material of both the shafts is same i.e. permissible shear stress is same
∴T ∝d^3
TA/TB =2^3/1^3 =8
∴TA=8TB

S10. Ans.(d)
Sol. Electro-hydraulic forming is a type of metal forming in which an electric arc discharge in liquid is used to convert electrical energy to mechanical energy and change the shape of the workpiece

Quiz:Mechanical Engineering 21 July 2020

Quiz: Mechanical Engineering
Exam: ISRO (TECHNICAL ASST.)
Topic: Miscellaneous

Each question carries 4 mark.
Negative marking: 1 mark
Time: 15 Minute

Q1. The entropy-increase of the solid substance as it melts into liquid at 27℃ (latent heat of fusion of substance = 300 kJ/kg)
(a) 14.8 kJ/kg-K
(b) 120 kJ/kg-K
(c) 10.8 kJ/kg-K
(d) 1 kJ/kg-K

Q2. The statement that molecular weight of all gases occupies the same volume is known as
(a) Avogadro’s hypothesis
(b) Gas law
(c) Dalton’s law
(d) Thermodynamics law

Q3. Critical speed of a turbine is
(a) same as run-away speed
(b) speed that will cause mechanical failure of the shaft
(c) speed at which natural frequency of vibrations equals the number of revolutions of the same time
(d) speed equal to synchronous speed of the generator

Q4. A curve showing the variation of load on a power station with respect to time is known as
(a) Load curve
(b) Load duration curve
(c) Diversity factor
(d) Performance curve

Q5. Problem of scavenging appears in case of
(a) Petrol engine
(b) Diesel engine
(c) Four-stroke engine
(d) Two-stroke engine

Q6. Consider the following statements with respect to evaporative cooling process:
1. The wet-bulb temperature remains constant.
2. The dew point temperature remains constant.
3. The enthalpy remains constant.
Which of the statements are correct?
(a) 1, 2 and 3
(b) 1 and 3 only
(c) 2 and 3 only
(d) 1 and 3 only

Q7. Select the correct statement:
(a) Viscosity of a gas increases with temperature
(b) Density of a gas increases with temperature
(c) Surface tension of a liquid increases with temperature
(d) Bulk modulus of elasticity is independent of temperature

Q8. The safeguarding structure provided in the dam to relieve the reservoir of excess water when the water level in the reservoir rises, is known as:
(a) Spillways
(b) Draft tube
(c) Catchment area
(d) Surge tank

Q9. The potential energy an elevator loses in coming down from the top of a building to stop at the ground floor is
(a) lost to the driving motors
(b) converted into heat
(c) lost in friction of the moving surface
(d) used up in lifting the counter poise weight

Q10. Which of the following is not an example of plastic?
(a) polyethylene, polystyrene
(b) Poly ethylene tetraphthalate
(c) Poly vinyl chloride
(d) Kovar

Solutions

S1. Ans (d)
Sol. We know that
Entropy-increase (∆S)=LH/T=300/300
= 1 kJ/kg-K

S2. Ans (a)
Sol. Avogadro’s law states that under the same conditions of temperature and pressure, equal volumes of different gases contain an equal number of molecules.

S3. Ans (c)
Sol. Critical speed is that speed of turbine at which speed of revolutions equals to natural frequency of revolutions of the system.

S4. Ans (a)
Sol. Load curve is the variation of load with time on a Power Station. As the load on a Power Station never remain constant rather it varies time to time, these variations in load is plotted on half hourly or hourly basis for the whole day. The curve thus obtained is known as Daily Load Curve.

S5. Ans (d)
Sol. Since, one engine cycle in a two-stroke engine is completed in one crankshaft rotation, gas exchange has to occur while the piston is near BDC. This process of simultaneously purging exhaust gas from the previous cycle and filling the cylinder with fresh charge for a new cycle is referred to as scavenging.

S6. Ans (d)
Sol. During evaporative cooling process, enthalpy and wet bulb temperature remains constant but DBT decreases and specific humidity along with relative humidity increases.

S7. Ans (a)
Sol. Viscosity of gas increases with temperature due to increase in momentum and viscosity of liquid decreases with temperature due to increases in molecular space.

S8. Ans (a)
Sol. A spillway is a structure used to provide the controlled release of flows from a dam or levee into a downstream area, typically the riverbed of the dammed river itself.

S9. Ans (d)
Sol. The potential energy an elevator loses in coming down from the top of a building to stop at the ground floor is used up in lifting the counter poise weight.

S10. Ans (d)
Sol. Kovar is not a type of plastic, but it is actually an iron nickel-cobalt alloy.

Quiz: Mechanical Engineering 17 July 2020

Quiz: Mechanical Engineering
Exam: ISRO (TECHNICAL ASST.)
Topic: Miscellaneous

Each question carries 4 mark.
Negative marking: 1 mark
Time: 15 Minute

Q1. Which one does not form a part of the gating system for a casting:
(a) Pouring basin
(b) Sprue
(c) Choke
(d) Pattern

Q2. Weld spatter defect in welding is generally the result of
(a) Using tool with high welding current
(b) Using tool with low welding current
(c) Low voltage
(d) High voltage

Q3. A good machinability rating would indicate:
(a) long tool life, high power requirement and less machining time
(b) long tool life, low power requirement and a good surface finish
(c) short tool life and a good surface finish
(d) long tool life, high power requirement and a good surface finish

Q4. Which one of the following devices produces incremental motion through equal pulses?
(a) AC servomotor
(b) DC servomotor
(c) Stepper motor
(d) Series motor

Q5. What is the preferred order of sequence for the following drives from high speed to low speed?
(a) Rack and pinion, spur gears, worm and worm wheel
(b) worm and worm wheel, spur gears, rack and pinion
(c) Worm and worm wheel, rack and pinion, spur gears
(d) Spur gears, worm and worm wheel, rack and pinion

Q6. If the angle of repose is 30°, the maximum efficiency of screw for motion up the inclined plane is:
(a) 50%
(b) 33.3%
(c) 75%
(d) None of these

Q7. The strain energy of the spring when it is subjected to the greatest load which the spring can carry without suffering permanent distortion is known as:
(a) Limiting stress
(b) Proof stress
(c) Proof resilience
(d) Proof load stress

Q8. A lead ball with a certain velocity is made to strike a wall, it falls down, but rubber ball of same mass and the same velocity strikes the same wall, it rebounds. Select the correct reason from the following:
(a) Both the balls undergo an equal change in momentum
(b) the change in momentum suffered by rubber ball is more than the lead ball
(c) the change in momentum suffered by rubber ball is less than the lead ball
(d) None of these

Q9. When the speed of a centrifugal pump is tripled, the power required to drive the pump will:
(a) Triple
(b) becomes 9 times
(c) becomes 27 times
(d) remains the same

Q10. Anything that generates entropy always:
(a) increases enthalpy
(b) decreases pressure
(c) decreases energy
(d) lowers chemical reaction

Solutions

S1. Ans (d)
Sol. Gating system has the following parts for a casting:
1. Pouring basin
2. Sprue
3. Choke

S2. Ans (a)
Sol. Weld spatter is usually seen when the welding voltage is too low or the amperage is too high for a given wire and gas combination.

S3. Ans (b)
Sol. Machinability index designates the degree of difficulty or ease with which a particular material can be machined. A good machinability rating or index represents long tool life, low power requirement and a good surface finish.

S4. Ans (c)
Sol. Stepper motors are DC motors that move in discrete steps. They have multiple coils that are organized in groups called phases. By energizing each phase in sequence, the motor will rotate, one step at a time.

S5. Ans (c)
Sol. The preferred order of sequence of the drives from high to low speed:
1. Worm and worm wheel
2. Rack and pinion
3. Spur gears

S6. Ans (b)
Sol. Given,
Angle of repose (θ) = 30°
Maximum efficiency of screw for motion up the inclined plane = (1-sinθ)/(1+sinθ)
= (1-sin30)/(1+sin30)
= 33.3%

S7. Ans (c)
Sol. Proof resilience is defined as the maximum energy that can be absorbed up to the elastic limit, without creating a permanent distortion.

S8. Ans (b)
Sol. As both lead and rubber balls have same mass and velocity, if rubber ball rebounds then there is more change in momentum of it than that of lead ball.

S9. Ans (c)
Sol. We know that
Power(P) ∝ Speed(N)^3
So, pump power requirement becomes 27 times the previous value.

S10. Ans (b)
Sol. If there is an entropy generation then definitely, there is a presence of temperature or pressure gradient. It means if pressure or temperature decreases then entropy generation takes place due to irreversibility.

Quiz:Mechanical Engineering 16 July 2020

Quiz: Mechanical Engineering
Exam: UPPSC AE
Topic: Thermal

Each question carries 3 mark.
Negative marking: 1 mark
Time: 10 Minute

Q1. In a steady flow process, across the control volume mass and energy flow
(a) Varies continuously
(b) Remains constant
(c) Depends on control surface
(d) Depends on type of process

Q2. Which of the following is correct statement?
(a) Entropy of isolated system always decreases
(b) Energy always degrades during the real process
(c) Energy always destroyed during the real process
(d) Heat transfer through a finite temperature difference is reversible process

Q3. Low grade waste heat in bottoming cycle of co-generation is used for:
(a) Feed water heating
(b) Processing
(c) Power generation
(d) None of these

Q4. High load factor indicates that
(a) cost of generation per unit power is increased
(b) total plant capacity is utilized for most of the time
(c) total plant capacity is not properly utilized for most of the time
(d) load on the plant is high

Q5. A 4-stroke reciprocating engine has 4-cylinders with diameter of 3 cm, stroke length of 8 cm and clearance volume 1 cc. The engine capacity in cc is:
(a) 110
(b) 252
(c) 400
(d) 227

Q6. The centrifugal compressors are generally used for refrigerants that require:
(a) Small displacement and low condensing pressures
(b) Large displacements and high condensing pressures
(c) Small displacements and high condensing pressures
(d) Large displacements and low condensing pressures

Q7. Amount of moisture that air can hold increases by:
(a) Decreasing both saturation pressure and temperature
(b) Decreasing saturation pressure and increasing temperature
(c) Increasing saturation pressure and decreasing temperature
(d) Increasing both saturation pressure and temperature

Q8. In transition boiling, heat flux decreases due to which of the following?
1. Low value of film heat transfer coefficient at the surface during 100℃ to 120℃ surface temperature.
2. Major portion of heater surface is covered by vapour film which has smaller thermal conductivity as compared to liquid.
3. Nucleate boiling occurs very fast.
Select the correct answer using the code given below.
(a) 1 only
(b) 2 only
(c) 3 only
(d) 1, 2 and 3

Q9. In which type of flow, the stream function satisfies the Laplace equation?
(a) Rotational flow crest
(b) Irrotational flow
(c) Circular flow
(d) None of these

Q10. Running cost of the hydro-electric power plant is
(a) more than the running cost of steam power plant
(b) less than the running cost of steam power plant
(c) equal to running cost of steam power plant
(d) equal to running cost of nuclear power plant

Solutions

S1. Ans.(b)
Sol. Following assumptions are made in steady flow process:
1. Control volume moves relative to the co-ordinate frame.
2. The state of the mass at each discrete area of flow on the control surface does not vary with time.

S2. Ans.(b)
Sol. Entropy of an isolated system always increases or remains constant, energy always degrades during a real process due to entropy generation, energy losses occur during a real process but energy remains conserved and heat transfer through a finite temperature difference is irreversible process.

S3. Ans.(a)
Sol. Low grade waste heat in the bottoming cycle of a combined cycle (co-generation) power plant is used for feed water heating for process use.

S4. Ans.(b)
Sol. Plant Load Factor (PLF) is the ratio of average power generated by the plant to the maximum power that could have been generated for a given time period. High load factor shows that total plant capacity is utilized for most of the time.

S5. Ans.(d)
Sol. Given,
Diameter (d) = 3 cm
Stroke length (L) = 8 cm
Clearance volume (Vc)= 1 cc
Engine capacity in cc = Swept volume× No. of cylinders
= π/4×d^2×L×4
= π/4×3^2×8×4
= 226.19 cc

S6. Ans.(d)
Sol. Centrifugal compressors are used for the applications where there is a requirement of high discharge and low condensing pressure.

S7. Ans.(b)
Sol. Air contains a certain amount of water vapor. The amount of water vapor any mass of air can contain depends on the temperature of that air i.e. the warmer the air is, the more water it can hold.

S8. Ans.(b)
Sol. As major portion of heater surface is covered by vapour film which has smaller thermal conductivity as compared to liquid, so heat flux decreases in transition boiling.

S9. Ans.(b)
Sol. The stream function is valid for two-dimensional flow. For irrotational flow, the stream function satisfies the Laplace equation.

S10. Ans.(b)
Sol. Hydro-electric power plant consumes no or negligible fossil fuels during its operation and it completely rely on hydro power. So, running cost of the hydro-electric power plant is less than the running cost of steam power plant.

Quiz: Mechanical Engineering 14 July 2020

Quiz: Mechanical Engineering
Exam: ISRO (TECHNICAL ASST.)
Topic: Miscellaneous

Each question carries 4 mark.
Negative marking: 1 mark
Time: 15 Minute

Q1. The shape and size of sand grains affects which of the following properties?
(a) Adhesiveness
(b) Porosity
(c) Refractoriness
(d) Strength

Q2. The percentage of carbon that must be present in steel before it can be hardened noticeably:
(a) 0.05
(b) 0.1
(c) 0.2
(d) 0.3

Q3. A master gauge is mainly used for which of the following purpose?
(a) checking thread cutting angle
(b) measuring internal diameter
(c) verifying the accuracy of gauges used on shop floor
(d) None of these

Q4. According to which law, for all perfect gases there is a change in volume by (1/273)th of their original volume at 0 deg C for every 1 deg C change in temperature when pressure remains constant.
(a) Joule’s law
(b) Boyle’s law
(c) Regnautt’s law
(d) Charles’ law

Q5. Which equation best represents the entropy (s) of a system with two parts with entropy x and y respectively?
(a) s = x + y
(b) s = x – y
(c) s < x + y
(d) s > x + y

Q6. Diesel cycle consists of which four processes?
(a) two isothermal and two isentropic processes
(b) two isentropic and two constant volume processes
(c) two isentropic, one constant volume and one constant pressure processes
(d) two isentropic and two constant pressure processes

Q7. Which of the following boiler is suitable to meet fluctuating demands?
(a) Babcock and Wilcox
(b) Locomotive
(c) Lancashire
(d) Cochran

Q8. Resilience of a material is important, if it is subjected to ______.
(a) Combined loading
(b) Fatigue
(c) Thermal stresses
(d) Shock loading

Q9. A balloon lifting in air follows the _______
(a) Law of gravitation
(b) Archimedes principle
(c) Principle of buoyancy
(d) All options are correct

Q10. In a single casing, multi-stage pump running at constant speed, the capacity rating is to be slightly lowered. It can be done by
(a) designing the new impeller
(b) trimming the impeller size to the required size by machining
(c) no means
(d) some other alterations in the impeller

Solutions

S1. Ans (b)
Sol. The shape and size of sand grains determine the porosity of the sand mould. If fine grain sand is used then porosity is less due to little space between sand particles and if coarse grain sand is used then porosity is high because of enough space between sand particles.

S2. Ans (d)
Sol. Low carbon steel which has 0.15 to 0.25% of carbon cannot be hardened by heating and subsequent quenching due to low carbon percentage. So, percentage of carbon must be about 0.3 % to get the steel hardened.

S3. Ans (c)
Sol. Master gauge is a very accurate gauge used only as a standard of reference for working gauges.

S4. Ans (d)
Sol. According to Charles’ law, for all perfect gases there is a change in volume by (1/273)th of their original volume at 0 deg C for every 1 deg C change in temperature when pressure remains constant.

S5. Ans (d)
Sol. Assume the combined system as isolated system. As entropy of an isolated system always increases, so s > x + y

S6. Ans (c)
Sol. A diesel cycle consists of four processes mainly:
1. Isentropic compression
2. Constant pressure heat addition
3. Isentropic expansion
4. Constant volume heat rejection

S7. Ans (b)
Sol. Locomotive boiler is a horizontal drum axis, multi-tubular, natural circulation, natural draft, solid fuel, fixed fire tube boiler. It is used to meet fluctuating demands.

S8. Ans (d)
Sol. When a material component is subjected to shock loading then a property comes into picture that is called resilience. Resilience is defined as the strain energy absorbed by the material within the elastic limit.

S9. Ans (d)
Sol. A balloon lifting in air follows law of gravitation, law of buoyancy or Archimedes principle for defining its equilibrium.

S10. Ans (b)
Sol. In a single casing, multi-stage pump running at constant speed, the capacity rating can be lowered by trimming the impeller size to the required size by machining.

Quiz: Mechanical Engineering 13 July 2020

Quiz: Mechanical Engineering
Exam: UPSSSC JE
Topic: Miscellaneous

Each question carries 1 mark
Negative marking: 1/4 mark
Time: 10 Minutes

Q1. What is the temperature at which a system goes under a reversible isothermal process without heat transfer?
(a) Absolute zero temperature
(b) Critical temperature
(c) Reversible temperature
(d) Boiling temperature

Q2. The property of a working system which changes as the heat is supplied to the working fluid in a reversible manner is known as-
(a) entropy
(b) enthalpy
(c) external energy
(d) internal energy

Q3. Which of the following cycles is not a reversible cycle?
1.Carnot
2.Ericsson
3.Stirling
4.Joule
(a) only A
(b) only A and B
(c) only C
(d) None of these

Q4. An engine indicator is used to determine the following
(a) Speed
(b) Temperature
(c) Indicative power
(d) None of these

Q5. Function of blow-down cock of a boiler is
(a) to maintain water level by draining excess water
(b) to empty the water drum of the boiler
(c) to remove sludge and sediments collected in drum
(d) to blow-off steam to maintain safe pressure

Q6. In a composite bar, the resultant strain produced will be-
(a) same as the strain produced in the bar
(b) sum of the strain produced by the individual bars
(c) same as the stress produced in each bar
(d) difference of strain produced in individual bars

Q7. Choose the correct option for the buckling load in a column to have the maximum value.
(a) Both ends of the column are fixed
(b) Both ends of the column are hinged
(c) One end of the column is clamped and the other end is free
(d) One end of the column is hinged and the other end is free

Q8. Which one of the following is the type of completely constrained motion?
(a) shaft in a circular hole
(b) shaft in a foot step bearing
(c) square bar in a square hole
(d) both shaft with collars in a circular hole and shaft in a foot step bearing

Q9. If a stiffer spring is used in Hartnell governor, then the governor will be-
(a) more sensitive
(b) less sensitive
(c) sensitivity remains unaffected
(d) isochronous

Q10. A fluid in which resistance to deformation is independent of the shear stress is called-
(a) Bingham plastic fluid
(b) Pseudo plastic fluid
(c) Dilatant fluid
(d) Newtonian fluid

Solutions

S1. Ans (a)
Sol. According to definition of Kelvin-scale, a system goes under a reversible isothermal process without heat transfer at the absolute temperature.

S2. Ans (a)
Sol. We know that
Change in entropy in reversible process (∆S)=∆Q/T
If heat is transferred in to the system then entropy change is positive and if heat is transferred out of the system then entropy change is negative.

S3. Ans (d)
Sol. Carnot, Ericsson, Stirling and Joule all are reversible cycles because all of the processes involved in these cycles are reversible.

S4. Ans (c)
Sol. An engine indicator diagram is a graph which is drawn between pressure and piston displacement through an engine stroke. Its area tells about the indicative power of the engine.

S5. Ans (c)
Sol. Due to continuous heating up and boiling of the water, sludge and sediments are collected at the inside walls of the tubes in case of water tube boilers. So, we use blow-down cock for periodical cleaning of the boiler to avoid overpressure and choking in the tubes.

S6. Ans (a)
Sol. In a composite bar, the resultant strain produced will be same as the strain produced in the bar from the compatibility equation.

S7. Ans (a)
Sol. We know that
Buckling load = (π^2 EI)/L^2
For both ends fixed effective length (L) = l/2
So, Buckling load = (4π^2 EI)/l^2 (Maximum)

S8. Ans (c)
Sol. When the components of a pair can have motion only in one direction with respect to each other then it is called completely constrained motion. E.g. square bar in a square hole etc.

S9. Ans (b)
Sol. If a stiffer spring is used in Hartnell governor, then the governor will be less sensitive. It is because the motion of the stiffer spring in response to change in speed of the engine is difficult.

S10. Ans (d)
Sol. A fluid in which resistance to deformation is independent of the shear stress is called Newtonian fluid. Here, resistance to deformation refers to viscosity of fluid.

Quiz: Mechanical Engineering 10th July 2020

Quiz: Mechanical Engineering
Exam: ISRO (TECHNICAL ASST.)
Topic: Miscellaneous

Each question carries 4 mark.
Negative marking: 1 mark
Time: 15 Minute

Q1. Consider the following energies associated with a Pelton turbine:
1. Mechanical energy
2. Kinetic energy
3. Potential energy
The correct sequence of energy conversion starting from the entry of fluid is
(a) 1, 2 and 3
(b) 2, 3 and 1
(c) 3, 2 and 1
(d) 1, 3 and 2

Q2. Consider the following statements:
1. Free expansion of a gas
2. Slow heating of oil from a constant temperature source
3. Evaporation of water at its saturation temperature by a source at the same temperature
4. Isentropic compression of an ideal gas
Which of these processes are irreversible?
(a) 1 and 2
(b) 2 and 3
(c) 3 and 4
(d) 1 and 4

Q3. The predominant forces acting on an element of fluid in the boundary layer over a flat plate placed in a uniform stream include.
(a) inertia and pressure forces
(b) viscous and pressure forces
(c) viscous and body forces
(d) viscous and inertia forces

Q4. Heat transfer takes place according to
(a) Zeroth law of thermodynamics
(b) first law of the thermodynamics
(c) second law of thermodynamics
(d) third law of thermodynamics

Q5. Bernoulli’s equation is applicable between any two points located in
(a) Rotational flow of an incompressible fluid
(b) Irrotational flow of compressible or incompressible flow
(c) Steady, rotational flow of an incompressible fluid
(d) Steady, irrotational flow of an incompressible fluid

Q6. Properties of substances like pressure, temperature and density in thermodynamic coordinates are
(a) path functions
(b) point functions
(c) cyclic functions
(d) real functions

Q7. While designing a cam, pressure angle is one of the most important parameters which is directly proportional to
(a) pitch circle diameter
(b) prime circle diameter
(c) lift of cam
(d) base circle diameter

Q8. The speed rating for turbine rotors is invariably more than √2 times its natural frequency to
(a) increase stability under heavy load and high speed
(b) isolate vibration of the system from the surrounding
(c) minimize deflection under dynamic loading as well as to reduce transmissibility of force to the surrounding
(d) None of the above

Q9. In circular arc cam with a flat faced reciprocating follower, the contact between the follower and the nose of cam is only maintained if:
(a) External spring force is less than the inertia force of the follower
(b) External spring force is greater than the inertia force of the follower
(c) External spring force is zero
(d) The inertia force is more than the spring force

Q10. Seam welding is
(a) multi-spot-welding process
(b) continuous spot-welding process
(c) used to form mesh
(d) used for welding cylindrical objects

SOLUTIONS

S1. Ans (c)
Sol. As water flows down the height its potential energy gets converted into kinetic energy, when water hits the runner, the kinetic energy gets converted into rotational mechanical energy of runner.

S2. Ans (d)
Sol.
(i) In isentropic compression process: Increase in entropy due to irreversibility is compensated by decrease in entropy due to heat loss and process becomes isentropic but not reversible.
(ii) Free expansion is always irreversible process due to absence of resistance against the expansion.
(iii) Slow heating is a quasi-static process which is reversible in nature.
(iv) Evaporation process is reversible.

S3. Ans.(d)
Sol. Reynolds number is used to characterize flow regimes, such as laminar flow and turbulent flow. It gives measure of the ratio of inertial force to viscous force. It consequently quantities the importance of boundary layer concept

S4. Ans.(c)
Sol. Heat transfer takes place according to second law of thermodynamics
Second law of thermodynamics states that “Heat will flow naturally from one reservoir to another at a lower temperature, but not in opposite direction without assistance”.

S5. Ans (d)
Sol. Bernoulli’s equation is applicable between any two points located in Steady, irrotational flow of an incompressible fluid.

S6. Ans.(b)
Sol. Properties of substances like pressure, temperature and density in thermodynamic coordinates are point functions.

S7. Ans.(d)
Sol. While designing a cam, pressure angle is one of the most important parameters which is directly proportional to base circle diameter.

S8. Ans.(b)
Sol. The speed rating for turbine rotors is invariably more than √2 times its natural frequency to isolate vibration of the system from the surrounding.

S9. Ans.(b)
Sol. When the cam contact force goes to zero, the cam and follower will separate. Large enough spring force is necessary to keep cam and follower in contact throughout the entire rotation. External spring force should be greater than inertia force of the follower to maintain positive contact. If external spring force is too large, there is possibility of higher contact stress leading to surface failure.

S10. Ans (b)
Sol. In seam welding overlapping sheets are gripped between two wheels or roller disc electrodes and current is passed to obtain either the continuous seam i.e. overlapping weld nuggets or intermittent seam i.e. weld nuggets are equally spaced. Welding current may be continuous or in pulses.

Quiz: Mechanical Engineering 9th July 2020

Quiz: Mechanical Engineering
Exam: UPPSC AE
Topic: Miscellaneous

Each question carries 3 mark.
Negative marking: 1 mark
Time: 10 Minute

Q1. In regarding nucleate boiling ___________
(a) The temperature of the surface is greater than the saturation temperature of the liquid
(b) Bubbles are created by expansion of entrapped gas or vapour at small cavities in the surface
(c) The temperature is greater than that of film boiling
(d) All options are correct

Q2. Calculate the power (in kW) required by the engine of a car travelling at the constant speed of 50 m/s. If the car has to resist a wind drag F_D=20V(in N), where V is the velocity of the car.
(a) 20
(b) 25
(c) 50
(d) 75

Q3. Water, by evaporating cooling, can be theoretically be cooled down to
(a) Atmospheric temperature
(b) Air dry bulb temperature
(c) Air wet bulb temperature
(d) Air dew point temperature

Q4. What is the location of frictional force when the intensity of pressure is uniform in a flat pivot bearing having radius r?
(a) r
(b) r/2
(c) 2r/3
(d) r/3

Q5. When the depth of water in an open channel is less than the critical depth, then flow is said to be
(a) critical
(b) turbulent
(c) torrential
(d) tranquil

Q6. In order that no shock wave develops when flow is taking place through a converging-diverging tube, Mach number at exit should be
(a) equal to 1
(b) greater than 1
(c) less than 1
(d) none of these

Q7. Which of the following is the correct method for the conversion of spring-controlled governor from unstable to stable?
(a) Increasing the ball weight
(b) Decreasing the spring stiffness
(c) Decreasing the ball weight
(d) Increasing the spring stiffness

Q8. Which one of the following assumptions in the theory of pure torsion is false?
(a) The angle of twist is uniform along the length
(b) The shaft is of uniform circular section throughout
(c) Cross-section plane before torsion remains plane after torsion
(d) All radii get twisted due to torsion

Q9. Filling or decking in a cooling tower increases the rate of heat transfer by providing
(a) increased flow of water
(b) increased flow of air
(c) increased flow of water and air
(d) a large amount of wetted surface

Q10. Two-stroke engines are used more frequently in two wheelers due to which of the following reasons?
(a) exhaust is less
(b) higher thermal efficiency
(c) higher power to weight ratio
(d) less friction

Solutions

S1. Ans.(a)
Sol. Nucleate boiling is a type of boiling that takes place when the surface temperature is hotter than the saturated fluid temperature by a certain amount but where the heat flux is below the critical heat flux.

S2. Ans.(c)
Sol. We know that
Power required = F_D×V
= 20×V×V
= 20×50^2
= 50 kW

S3. Ans.(c)
Sol. By evaporating cooling, air can be cooled down to its wet bulb temperature. Evaporative cooling is a process that uses the effect of evaporation as a natural heat sink. Sensible heat from the air is absorbed to be used as latent heat necessary to evaporate water.

S4. Ans.(c)
Sol. The frictional force acts at 2r/3 distance from the center when intensity of pressure is given uniform.

S5. Ans.(c)
Sol. When the depth of water in an open channel is less than the critical depth, then flow is said to be torrential.

S6. Ans.(b)
Sol. Mach number at exit should be greater than 1 for no shock wave generation when flow is taking place through a converging-diverging tube.

S7. Ans.(b)
Sol. A spring-controlled governor is said to be stable if the radius of the balls increases with increase in the speed of the governor and vice versa. A spring-controlled governor can be made stable by decreasing the spring stiffness.

S8. Ans.(a)
Sol. Following assumptions are made in the theory of pure torsion:
The material of shaft is uniform throughout
The shaft is of uniform circular cross-section throughout its length
Cross section remains plane before and after torsion.
All radii get twisted due to torsion

S9. Ans.(d)
Sol. Filling or decking in a cooling tower increases the rate of heat transfer by providing increased wetted area.

S10. Ans.(c)
Sol. Two-stroke engines are used more frequently in two wheelers due to higher power to weight ratio of these engines.

Quiz: Mechanical Engineering 07 July 2020

Quiz: Mechanical Engineering
Exam: ISRO (TECHNICAL ASST.)
Topic: Miscellaneous

Each question carries 4 mark.
Negative marking: 1 mark
Time: 15 Minute

Q1. Plastic toys are usually produced by using:
(a) Shell moulding
(b) Green sand moulding
(c) Plaster moulding
(d) Injection moulding

Q2. Austenite is a solid solution of carbon in________iron.
(a) Alpha
(b) Beta
(c) Gamma
(d) Delta

Q3. Boyle’s law i.e. pV = constant is applicable to gases under
(a) all ranges of pressure
(b) only small range of pressures
(c) high range of pressures
(d) steady change of pressures

Q4. In a cyclic process, the work done by the system is 20 kJ, -30 kJ, -5 kJ and 10 kJ. What is the net-heat transfer(kJ) for the cyclic process?
(a) -5
(b) 0
(c) 5
(d) 10

Q5. Stirling and Ericsson cycles are
(a) reversible cycles
(b) irreversible cycles
(c) quasi-static cycles
(d) semi-reversible cycles

Q6. The dry saturated steam at very low pressure, (5 – 10 kg/cm^2) when throttled to atmosphere will become
(a) wet
(b) superheated
(c) remain dry saturated
(d) dry

Q7. Which of the following statement is correct for the modulus of resilience?
(a) It is the ratio of maximum stress energy and unit volume
(b) It is the ratio of maximum strain energy and unit volume
(c) It is the ratio of proof resilience and unit volume
(d) It is the ratio of proof resilience and unit area

Q8. In gears, interference takes place when______
(a) Tip of tooth of a mating gear digs into the portion between base and root circles
(b) Gears do not move smoothly in the absence of lubrication
(c) Pitch of the gear is not same
(d) Gear teeth are undercut

Q9. For a submerged curved surface, the component of force due to static liquid is equal to _______
(a) Weight of the liquid supported by curved surface
(b) Force on a projection of the curved surface on a vertical plane
(c) Area of curved surface × pressure at the centroid of the submerged area
(d) None of these

Q10. Anti-friction bearings are:
1. Sleeve bearings
2. Hydrodynamic bearings
3. Thin lubricated bearings
4. Ball and roller bearings
(a) only A
(b) only B and C
(c) only C
(d) only D

Solutions

S1. Ans (d)
Sol. Injection moulding is a method to obtain molded products by injecting plastic materials melted by heat into a mould, and then cooling and solidifying them. The method is suitable for the mass production of products with complicated shapes, and takes a large part in the area of plastic processing.

S2. Ans (c)
Sol. Austenite is a solid solution of carbon in gamma iron. The solid solution of carbon in a non-magnetic form of iron is stable at high temperatures. It is a constituent of some forms of steel.

S3. Ans (b)
Sol. All gas laws are applicable for ideal gases or the gases at high temperature and low pressure.

S4. Ans (a)
Sol. We know that
First law of thermodynamics ∮dQ=∮dW
So, net heat transfer = 20-30-5+10 = -5 kJ

S5. Ans (a)
Sol. Stirling and Ericsson cycles both are reversible cycles. Stirling cycle has constant volume heat addition and rejection and Ericsson cycle has constant pressure heat addition and rejection.

S6. Ans (a)
Sol. The dry saturated steam at very low pressure, (5 – 10 kg/cm^2) when throttled to atmosphere will become wet.

S7. Ans (c)
Sol. The modulus of resilience is the maximum amount of energy per volume that a material can absorb while elastically deforming.

S8. Ans (a)
Sol. In gears, interference takes place when tip of tooth of a mating gear digs into the portion between base and root circles.

S9. Ans (a)
Sol. For a submerged curved surface, the component of force due to static liquid is equal to weight of the liquid supported by curved surface up to the free surface of liquid.

S10. Ans (d)
Sol. An anti-friction bearing, also known as a rolling contact bearing, is justified over a journal or fluid film bearing when very little friction is needed for low differential. E.g. Ball and roller bearing etc.

Quiz: Mechanical Engineering 06 July 2020

Quiz: Mechanical Engineering
Exam: UPSSSC JE
Topic: Miscellaneous

Each question carries 1 mark
Negative marking: 1/3 mark
Time: 10 Minutes

Q1. Frictional losses in the nozzle
(a) reduces the enthalpy of the fluid
(b) increases the enthalpy of the fluid
(c) no effect on enthalpy of the fluid
(d) None of the above
L1Difficulty 3
QTags Mechanical
QCreator Paper Maker 10

Q2. The pressure centre is
(a) the centroid of the pressure prism
(b) a point on the line of action of the resultant force
(c) at the centroid of the submerged area
(d) always above the centroid of the area
L1Difficulty 3
QTags Mechanical
QCreator Paper Maker 10

Q3. Match List-I (Stability) and List-II (Conditions) and select the correct answer using the codes given below the lists:
List-I
A. Stable equilibrium of a floating body
B. Stable equilibrium of a submerged body
C. Unstable equilibrium of a floating body
D. Unstable equilibrium of a submerged body
List-II
1. Centre of buoyancy below the centre of gravity
2. Metacentre above the centre of gravity
3. Centre of buoyancy above the centre of gravity
4. Metacentre below the centre of gravity
Codes:
A B C D
(a) 4 3 2 1
(b) 2 3 4 1
(c) 4 1 2 3
(d) 2 1 4 3
L1Difficulty 3
QTags Mechanical
QCreator Paper Maker 10

Q4. Which phenomenon will occur when the valve at the discharge end of a pipe connected to a reservoir is suddenly closed?
(a) Cavitation
(b) Erosion
(c) Hammering
(d) Surging
L1Difficulty 3
QTags Mechanical
QCreator Paper Maker 10

Q5. When a system reaches the state of equilibrium, the following property assumes its maximum value
(a) Availability
(b) Entropy
(c) Gibbs function
(d) Helmholtz function
L1Difficulty 3
QTags Mechanical
QCreator Paper Maker 10

Q6. In centrifugal compressor terminology, vaneless space refers to the space between
(a) The inlet and blade inlet edge
(b) Blades in the impeller
(c) Diffuser exit and volute casing
(d) Impeller tip and diffuser inlet edge
L1Difficulty 3
QTags Mechanical
QCreator Paper Maker 10

Q7. In a single-stage open-cycle gas turbine, the mass flow through the turbine is higher than the mass flows through compressor, because
(a) the specific volume of air increases by use of intercooler
(b) the temperature of air increases in the reheater
(c) the combustion of fuel takes place in the combustion chamber
(d) the specific heats at constant pressure of incoming air and exhaust gases are
different
L1Difficulty 3
QTags Mechanical
QCreator Paper Maker 10

Q8. For the same type of shapes, the value of Radiation Shape Factor will be higher when surfaces are
(a) More closer only
(b) Moved further apart
(c) Smaller and held closer
(d) Larger and held closer
L1Difficulty 3
QTags Mechanical
QCreator Paper Maker 10

Q9. In aircraft, air refrigeration cycle is used because of
(a) low unit weight per tonne of refrigeration
(b) high heat transfer rate
(c) lower temperature at thigh-altitudes
(d) higher coefficient of performance
L1Difficulty 3
QTags Mechanical
QCreator Paper Maker 10

Q10. The optimum effective temperature for human comfort is
(a) higher in winter than that in summer
(b) lower in winter than that in summer
(c) same in winter and summer
(d) not dependent on season
L1Difficulty 3
QTags Mechanical
QCreator Paper Maker 10

SOLUTIONS

S1. Ans (a)
Sol. Frictional losses in the nozzle reduces the enthalpy of the fluid.

S2. Ans (b)
Sol. The center of pressure is the point on a body where the total sum of a pressure field acts, causing a force and no moment about that point.

S3. Ans (b)
Sol.
(a) Stable equilibrium of floating body: Metacentre above the centre of gravity.
(b) Stable equilibrium of submerged body: Centre of buoyancy above the centre of gravity.
(c) Unstable equilibrium of a body floating: Metacentre below the centre of gravity.
(d) Unstable equilibrium of a submerged body: Centre of buoyancy below the centre of gravity.

S4. Ans (c)
Sol. When water flowing in a long pipe is suddenly brought to rest by c losing the valve or by any similar cause there will be a sudden rise in pressure due to momentum of the moving water being destroyed this causes a wave of high pressure to be transmitted along the pipe which creates noise called as knocking. This phenomenon of sudden rise in pressure in the pipe is called as water hammer or hammer blow.

S5. Ans (b)
Sol. When system reaches equilibrium, driving force that executed the process becomes zero and entropy attains its maximum value. Moreover as the process progress towards equilibrium the available energy or availability decreases continuously.

S6. Ans (d)
Sol. In centrifugal compressor terminology, vaneless space refers to the space between Impeller tip and diffuser inlet edge.

S7. Ans (c)
Sol. After the compression of air, same amount of fuel is added in the combustion chamber which undergoes combustion. After combustion the flue gases are expanded in the turbine which is more than the mass flow rate of only air in the compressor.

S8. Ans(d)
Sol. The value of radiation shape factor is high if surfaces are large and closer to each other.

S9. Ans.(a)
Sol. In aircraft, air refrigeration cycle is used because of low unit weight per ton of refrigeration. It is becoming obsolete because of their low coefficient of performance and high power requirements.

S10. Ans.(b)
Sol. In winter the optimum effective temperature is 19°C where as in summer this temperature is 22°C.

Quiz: Mechanical Engineering 03 July 2020

Quiz: Mechanical Engineering
Exam: ISRO (TECHNICAL ASST.)
Topic: Miscellaneous

Each question carries 4 mark.
Negative marking: 1 mark
Time: 15 Minute

Q1. The main advantage of shell moulding is that:
(a) a metallic pattern is used
(b) the moulds are stronger
(c) thin sections can be easily obtained
(d) high production rate is possible

Q2. Boring can be performed by
(a) boring machines only
(b) boring machines and lathe
(c) a machine only by single point high speed carbide tools
(d) boring machine, lathe and milling machine

Q3. Three states of matter are distinguished with respect to molecules by the
(a) Atoms in molecules
(b) Number
(c) Orientation
(d) Character of motion

Q4. The flow through a turbine in Mollier diagram is represented by a
(a) curved line convex up
(b) curved line convex down
(c) horizontal line
(d) vertical line

Q5. For the same output, same speed and same compression ratio, the thermal efficiency of a two-stroke cycle petrol engine as compared to that for four-stroke petrol engine is:
(a) Same as long as output is same
(b) More
(c) Same as long as compression ratio is same
(d) Less

Q6. The solid fuel having the highest calorific value is
(a) wood
(b) lignite
(c) coke
(d) anthracite

Q7. Which of the following is correct for validation of Hook’s law in simple tension test?
(a) Ultimate stress
(b) Breaking point
(c) Elastic limit
(d) Limit of proportionality

Q8. The mechanism obtained by fixing the sliding pair in single slider crank mechanism is:
(a) Bull engine
(b) Oscillating cylinder engine
(c) Gnome engine
(d) Crank and slotted lever quick return mechanism

Q9. A body is vibrating at 10 vibrations/second in simple harmonic motion of 10 cm amplitude. Th maximum velocity in cm/sec can be
(a) 100π
(b) 50 π
(c) 200 π
(d) 100 π

Q10. In an isothermal atmosphere, the pressure
(a) decreases linearly with elevation
(b) remains constant
(c) varies in the same way as the density
(d) increases exponentially with elevation

Solutions

S1. Ans (d)
Sol. The main advantages of shell moulding casting:
1.Good surface quality
2.High dimensional accuracy
3.Thin wall thickness and complex casting can be made
4.Less manpower and molding are required
5.High production rate

S2. Ans (d)
Sol. Boring is the process of enlarging a hole that has already been drilled (or cast) by means of a single-point cutting tool. It can be done by using boring machine, lathe and milling machine. Good surface finish is obtained in boring machine and lathe machine but not by milling machine due to intermittent cuts.

S3. Ans (d)
Sol. The states of matter are characterized by the motion of molecules in matter. There are three main states of matter i.e. solid, liquid and gas.

S4. Ans (d)
Sol. On Mollier diagram, the flow through a turbine is represented by a vertical line.

S5. Ans (d)
Sol. As losses of fuel in exhaust is high. So, for the same output, same speed and same compression ratio, the thermal efficiency of a two-stroke cycle petrol engine as compared to that for four-stroke petrol engine is less.

S6. Ans (d)
Sol. Anthracite is high rank coal used for industrial and residential applications. It has generally less than 10% volatile matter and a high carbon content (about 90% fixed carbon). Its gross calorific value is equal to or greater than 24 000 kJ/kg on an ash-free but moist basis.

S7. Ans (d)
Sol. Hook’s law is valid up to proportional limit. It states that the strain in a solid is proportional to the applied stress within the elastic limit or up to limit of proportionality of that solid.

S8. Ans (a)
Sol. Bull engine is the fourth inversion of single slider crank mechanism which is obtained when the slider is fixed.

S9. Ans (c)
Sol.
Given,
Amplitude (A) = 10 cm
Vibration speed (N) = 10 vibration/sec
Maximum velocity (Vmax)=A×2πN/60
=10×2π×10=200π

S10. Ans (a)
Sol. In an isothermal atmosphere, the pressure decreases exponentially upward.

Quiz: Mechanical Engineering 02 July 2020

Quiz: Mechanical Engineering
Exam: UPPSC AE
Topic: Miscellaneous

Each question carries 3 mark.
Negative marking: 1 mark
Time: 10 Minute

Q1. What is the main function of chaplets?
(a) It ensures directional solidification just like chills
(b) It provides efficient venting
(c) It supports the core
(d) It joins lower and upper parts of the moulding sand

Q2. Graphite mould are generally used for continuous casting method because
(a) The metals wet the mould slightly
(b) They are self-lubricating
(c) Only a small amount of lubricating oil is required
(d) They are comparatively cheaper

Q3. The soldering iron is heated in gas flame until
(a) the bit is the red hot
(b) the coating of Borax on the bit turns black
(c) the gas flame appears orange in the colour
(d) the gas flame appears green in the colour

Q4. When turning a long shaft on a lathe, its bending can be prevented by:
(a) running the shaft at low speed
(b) using sturdy machine
(c) using high speed
(d) using steady rest

Q5. As per Indian standard specifications, a plain carbon steel designated as 40C8 contains ___________ % of carbon.
(a) 0.4 to 0.6
(b) 0.04
(c) 0.6 to 0.8
(d) 0.35 to 0.45

Q6. For which of the following products, the LD converter is used?
(a) steel
(b) polythene
(c) graphite
(d) cast iron

Q7. Which of the following is a non-quasi-static process?
(a) Free expansion of a gas
(b) Expansion of a gas in a cylinder under constant pressure
(c) Rapid compression of a gas in a cylinder
(d) Gradual compression of a gas in a cylinder

Q8. Which of the following statements is incorrect regarding a four-stroke engine as compared to a two-stroke engine?
(a) It requires a heavier foundation
(b) It can be easily started
(c) More cooling time is available
(d) It occupies more space

Q9. What is the unsteady to and fro motion of the fluid that causes pulsation in the engine compressor known as?
(a) Compressing
(b) Pulsing
(c) Choking
(d) Surging

Q10. Radius of curvature of a stressed beam and modulus of elasticity
(a) are directly proportional
(b) are inversely proportional
(c) are curvilinear related
(d) have unpredictable relationship

Solutions

S1. Ans.(c)
Sol. Chaplets are used to position and support the core.

S2. Ans.(b)
Sol. Graphite is a self-lubricating which creates low friction between the mould surface and the solidifying metal; ensuring smooth extraction of the casting without cracks.

S3. Ans.(a)
Sol. A soldering iron is a hand tool used in soldering. It supplies heat to melt solder so that it can flow into the joint between two work pieces. The soldering iron is heated in gas flame until it becomes red.

S4. Ans.(d)
Sol. When turning a long shaft on a lathe, its bending can be prevented by using steady rest.

S5. Ans.(d)
Sol. As per Indian standard specifications, a plain carbon steel designated as 40C8 contains 0.35 to 0.45 % carbon.

S6. Ans.(a)
Sol. Basic oxygen steel-making process also known as Linz–Donawitz-steel-making or the oxygen converter process. This is used for steel products.

S7. Ans.(a)
Sol. Free expansion of a gas is a non-quasi-static or irreversible process.

S8. Ans.(b)
Sol. Two stroke engine is easier to start when as compared to four stroke engines. Four-stroke engines require two complete turns of the crankshaft to make a power stroke, compared to the single turn necessary in a two-stroke engine. Cold starting is also easier in two stroke engines i.e. why it is used in snowmobiles.

S9. Ans.(d)
Sol. There is an unstable limit of operation of centrifugal and axial flow compressor, known as surging. Surging is caused due to unsteady, periodic and reversal of flow through the compressor when the compressor has to operate at less mass flow rate than a predetermined value.

S10. Ans.(a)
Sol. From bending-moment equation,
M/I=σ/Y=E/R
So,
E∝R

Quiz: Mechanical Engineering 30 June 2020

Quiz: Mechanical Engineering
Exam: ISRO (TECHNICAL ASST.)
Topic: Miscellaneous

Each question carries 4 mark.
Negative marking: 1 mark
Time: 15 Minute

Q1. Which one of the following are intensive properties?
1.Kinetic energy
2.Specific entropy
3.Pressure
4.Enthalpy
Codes:
(a) 1 and 3
(b) 2 and 3
(c) 1,3 and 4
(d) 2 and 4

Q2. It is desired to bring about a change in the state of a system by performing work on the system under adiabatic conditions.
(a) The amount of work needed is path dependent
(b) Work alone cannot bring about such a change of state
(c) The amount of work needed is independent of path
(d) More information is needed to conclude anything about the path dependence or otherwise of the work needed

Q3. ‘’Heat cannot be transported from a system at low temperature to another system at high temperature without the aid of external agency’’. This statement of second law is attributed to
(a) Clausius
(b) Joule Thomson
(c) Max Planck
(d) Gay-Lussac

Q4. In statistical thermodynamics, entropy is defined as
1.measure of irreversibility of a system
2.a universal property
3.degree of randomness
4.thermodynamic probability of disorderness
Which of the above is/are correct?
(a) 1 and 3
(b) 1, 2 and 3
(c) 2, 3 and 4
(d) 1, 3 and 4

Q5. Availability of a system at any given state is
(a) a property of a system
(b) the total energy of the system
(c) the maximum work obtainable as system goes to dead state
(d) the maximum useful work obtainable as the system goes to dead state

Q6. Change of state e.g. freezing, melting, evaporation and condensation is an
(a) Adiabatic process
(b) Isopiestic process
(c) Isothermal process
(d) Isochoric process

Q7. For an ideal gas the value of Joule-Thomson coefficient is
(a) zero
(b) 0.5
(c) unity
(d) infinite

Q8. When a gas is to be stored, the type of compression that would be ideal is
(a) Isothermal
(b) Adiabatic
(c) Polytropic
(d) Constant volume

Q9. Gibb’s free energy (G) is given by
(a) G=H-TS
(b) G=H/TS
(c) G=U-TS
(d) None of these

Q10. Thermo-electric refrigeration is based on
(a) Peltier effect
(b) Joule effect
(c) Joule-Thomson throttling
(d) Adiabatic demagnetization

Solutions

S1. Ans.(b)
Sol. Intensive properties are those properties which do not depend on mass e.g. pressure, temperature, all specific properties etc.

S2. Ans.(a)
Sol. The amount of work needed is path dependent always.

S3. Ans.(a)
Sol. According to Clausius statement of second law of thermodynamics, ‘’ heat cannot be transferred from a lower temperature to higher temperature without the aid of external agency.’’

S4. Ans.(d)
Sol. Entropy is a measure of irreversibility in the system, it is a degree of randomness and probability of disorderness in the system.

S5. Ans.(d)
Sol. Availability of a system at any given state is the maximum useful work obtainable as the system goes to dead state.

S6. Ans.(b)
Sol. Freezing, melting, evaporation and condensation all are phase changing process. All the phase change take place at constant pressure process.

S7. Ans.(a)
Sol. Joule-Thomson coefficient (μ) for an ideal gas =0

S8. Ans.(a)
Sol. Isothermal compression is an ideal process for compressed air storage because this process consumes the least work.

S9. Ans.(a)
Sol. Gibb’s free energy function is given by G=H-TS

S10. Ans.(a)
Sol. Thermo-electric refrigeration works on the principle of Peltier effect.