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.

Quiz:Mechanical Engineering 29 June 2020

Quiz: Mechanical Engineering
Exam: UPSSSC JE
Topic: Miscellaneous

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

Q1. Young’s modulus (E), Bulk modulus (K) and Shear modulus (G) are related by
(a) E=(K+G)/6K
(b) E=9KG/(3K+G)
(c) E=(9K+G)/6K
(d) E=(K+6G)/6K

Q2. Open circuit test on the transformer is to measure its
(a) Copper loss
(b) Leakage reactance
(c) Equivalent impedance
(d) Core loss

Q3. Number of minimum control points required to generate a quadratic B-spline curve
(a) 2
(b) 3
(c) 4
(d) 5

Q4. Which is a positive drive?
(a) Flat belt drive
(b) Round belt drive
(c) Crossed belt drive
(d) Timing belt

Q5. De-aerator in thermal power plants is used to
(a) Remove dissolved gases from feed water
(b) Reduce temperature of feed water
(c) Reduce pressure of feed water
(d) None of the above

Q6. When the state is being changed from gas to liquid state through the process of condensation, the temperature?
(a) increases
(b) decreases
(c) remains constant
(d) may increase or decrease

Q7. Air refrigeration system operates on
(a) Carnot cycle
(b) Rankine cycle
(c) Reversed Carnot cycle
(d) Bell Coleman cycle

Q8. High API gravity of fuel means:
(a) Lower Diesel index
(b) Lower Brake specific fuel consumption
(c) Lower heat of combustion
(d) Lower ignition quality

Q9. A refrigerant should have:
(a) High specific heat of liquid
(b) High boiling point
(c) High latent heat of vaporization
(d) Low critical temperature

Q10. Lumped heat capacity approach of transient heat conduction analysis is used:
(a) For bodies of very high conductive resistance
(b) When temperature variation throughout the body is very high
(c) When temperature variation throughout the body is very low
(d) For Biot number > 5

Solutions

S1. Ans (b)
Sol. Relation between E, K and G is
E=9KG/(3K+G)

S2. Ans (d)
Sol. The purpose of the open-circuit test is to determine the no-load current and losses of the transformer because of which their no-load parameters are determined. The core loss of the transformer can be determined by this test.

S3. Ans (b)
Sol. B-splines are a more general type of curve than Bezier curves. In a B-spline each control point is associated with a basis function. If the order of B-spline is n then we require (n+1) control points to generate B-spline. So, for quadratic B-spline, we need 3 control points.

S4. Ans (d)
Sol. As slip occurs in other given options, so these all are negative drive except timing belt.

S5. Ans (a)
Sol. De-aerator is fixed with the feed water tank of the boiler in power plants. It is used to remove dissolved gases from the water, which otherwise, causes reduction in heat transfer in the boiler and oxidation in the tubes of the boiler.

S6. Ans (c)
Sol. Temperature and pressure both remain constant in all the phase changing processes. Such as condensation, boiling, freezing etc. In the condensation process, heat of vaporization is released and vapor is converted into liquid.

S7. Ans (d)
Sol. Bell-Coleman cycle is an air refrigeration cycle. It uses air as refrigerant and this cycle is majorly used in aircrafts due to low weight per ton of refrigeration.

S8. Ans (b)
Sol. API stands for American Petroleum institute. API gravity is a measure of how heavy or light a petroleum liquid is as compared to water. High API gravity of fuel represents lower brake specific fuel consumption.

S9. Ans (c)
Sol. There are following properties of a good refrigerant:
1.Low boiling point.
2.Low freezing point
3.High latent heat of vaporization
4.Low viscosity
5.Low specific volume
6.High critical temperature

S10. Ans (c)
Sol. Lumped heat capacity approach of transient heat conduction analysis is used when conductive resistance of the body is negligible and hence, the variation in temperature throughout the body is also negligible.

Quiz:Mechanical Engineering 26 June 2020

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

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

Q1. Which one of the following is not related to a compression ignition engine?
(a) Fuel pump
(b) Fuel injector
(c) Governor
(d) Carburetor

Q2. Gradually increasing temperature of flue gases at inlet to chimney for given steam output is a sign 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. If the sensible heating of air is taken place over a coil, then the coil efficiency in terms of B.P.F (Bypass factor) is
(a) B.P.F.-1
(b) 1+B.P.F.
(c) 1-B.P.F.
(d) B.P.F.+1

Q4. What type of rotary compressor is used in aeroplanes?
(a) Centrifugal type
(b) Radial flow type
(c) Axial flow type
(d) None of these

Q5. Indicator diagram of a reciprocating pump is a graph plotted between
(a) Pressure in cylinder vs swept volume
(b) Flow vs swept volume
(c) Pressure vs speed
(d) Flow vs speed

Q6. Following assumptions are made in Bernoulli’s equation:
(a) There is no loss of energy of the liquid flowing
(b) Only gravity force acts on the fluid
(c) The velocity of flow is uniform across any cross-section of the pipe
(d) All of these

Q7. In which of the following heat is transferred by radiation?
(a) Heating of building
(b) Cooling of parts in furnace
(c) Blast furnace
(d) Heat received by a person from fireplace

Q8. 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

Q9. Producer gas is obtained by
(a) Partial combustion of coal, coke, anthracite coal or charcoal in a mixed air steam blast
(b) Passing steam over incandescent coke
(c) Carbonisation of bituminous coal
(d) Passing air and a large amount of steam over waste coal at about 700 Deg C

Q10. Which of the following law governs the heating of a gas at constant volume?
(a) Charles’ law
(b) Gay-Lussac law
(c) Boyle’s law
(d) Avogadro’s law

Solutions

S1. Ans (d)
Sol. Carburetor is used in Spark-ignition engine. It is a device which is used to form a mixture of air and fuel in a required proportion as per vehicle running conditions.

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 (c)
Sol. Coil efficiency or contact factor is defined as the fraction of air passing over the coil while contacting the coil surface.
If B.P.F. is bypass factor then coil efficiency or contact factor=1-B.P.F.

S4. Ans (c)
Sol. Axial flow type air compressor is used in aeroplanes. Axial flow type air compressor gives high head and low discharge flow.

S5. Ans (a)
Sol. Indicator diagram is plotted between mean effective pressure and swept volume of reciprocating engine.

S6. Ans (d)
Sol. Bernoulli’s equation is based on the following assumptions:
1.Steady flow
2. Incompressible fluid
3.No loss of energy
4.Only gravity force is in picture
5.Uniform velocity across any cross-section

S7. Ans (d)
Sol. Heat received by a person from fireplace is the case of heat transfer by radiation.

S8. Ans (b)
Sol. For an ideal reflector, the energy distribution at higher temperature is largely in the range of shorter wavelength.

S9. Ans (a)
Sol. Production of producer gas is done by partial combustion of coal, coke, anthracite coal or charcoal in a mixed air steam blast.

S10. Ans (b)
Sol. Gay-Lussac’s law states that at constant volume, absolute pressure of an ideal gas is proportional to the temperature of the gas.
i.e. P/T=Constant (At constant volume)

Quiz: Mechanical Engineering 25 June 2020

Quiz: Mechanical Engineering
Exam: UPPSC AE
Topic: Thermal

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

Q1. A jet engine has
(a) No propeller
(b) Propeller in front
(c) Propeller at back
(d) Propeller on the top

Q2. In a uni-flow engine
(a) Steam enters and exhausts through the same port
(b) Steam enters at one end and exhausts at the center
(c) Steam enters at the center and exhausts at the other end
(d) None of the above

Q3. Specific heat of air increases with increase in
(a) Temperature
(b) Pressure
(c) Both pressure and temperature
(d) Variations of its constituents

Q4. The variables which control the physical properties of a perfect gas are
(a) Pressure exerted by the gas
(b) Volume occupied by the gas
(c) Temperature of the gas
(d) All of the above

Q5. Total emissivity of polished silver surface as compared to black surface is
(a) Same
(b) More or less same
(c) less
(d) Very much lower

Q6. The region between the separated streamline and the boundary surface of the solid body after separation is known as
(a) Drag
(b) Wake
(c) Lift
(d) Boundary layer

Q7. A true one-dimensional flow occurs when
(a) The direction and magnitude of the velocity at all points are identical
(b) The magnitude and direction of the velocity do not change from point to point in the fluid
(c) The velocity of successive fluid particles, at any point is the same at successive periods of time
(d) The fluid particles move in plane or parallel planes and the streamline patterns are identical to each other

Q8. Which of the following hydraulic unit is used to transmit increased or decreased torque to driven-shaft?
(a) Hydraulic torque converter
(b) Hydraulic intensifier
(c) Hydraulic ram
(d) Hydraulic accumulator

Q9. At lower temperature and pressures, the latent heat of vaporization of a refrigerant
(a) increases
(b) decreases
(c) remains same
(d) None of these

Q10. Which of the following will reduce volumetric efficiency of a vertical CI engine?
(a) Inlet valve closing before BDC
(b) Inlet valve closing after BDC
(c) Inlet valve opening before TDC
(d) Exhaust valve closing after TDC

Solutions

S1. Ans.(a)
Sol. A jet engine is a type of reaction engine. It produces thrust by jet propulsion by discharging a fast-moving jet.

S2. Ans.(b)
Sol. In a uni-flow engine, steam enters at one end and exhaust at the center.

S3. Ans.(a)
Sol. Specific heat of air increases with increase in temperature because at elevated temperatures, one or more constituents of air will gain more degrees of freedom, which allows them to store more heat. This, in turn, means that more heat should be supplied for the temperature change.

S4. Ans.(d)
Sol. According to ideal gas equation,
PV=nRT
Here,
P = Pressure exerted by the gas
V = volume occupied by the gas
T = Temperature of the gas
So, physical properties of a perfect or ideal gas are dependent on P, V, T of the gas.

S5. Ans.(d)
Sol. Polished surface emissivity (0.02) is much lower than that of black surface (0.97) at room temperature.

S6. Ans.(b)
Sol. The space or region between separated streamline and boundary surface is known as wake. In the wake, so much dissipation of energy takes place and it is an undesirable phenomenon due to the same reason.

S7. Ans.(a)
Sol. When the direction and magnitude of the velocity at all points are identical, then it is known as true one-dimensional flow.

S8. Ans.(a)
Sol. Torque converter is a fluid coupling in which three or more rotors are used, one of which can be checked so that output torque is augmented and output speed diminished and vice versa.

S9. Ans.(a)
Sol. As the temperature and pressure of refrigerant decreases then the refrigerant effect and latent heat of vaporization increase in a vapour compression refrigeration cycle.

S10. Ans.(a)
Sol. If inlet valve closes before BDC in CI engine then its volumetric efficiency decreases because of the less time available for charge(air) admission into the cylinder. For high volumetric efficiency, inlet valve should close after BDC.

Quiz: Mechanical Engineering 23 June 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 statements: An increase in pin fin effectiveness is caused by high value of
1. Convective coefficient
2. Thermal conductivity
3. Sectional area
4. Circumference
Which of the above statements are correct?
(a) 1 and 3
(b) 1 and 4
(c) 2 and 3
(d) 2 and 4

Q2. Ericsson Cycle consists of
(a) Two isochoric process and two isobars
(b) Two isothermal process and two isobars
(c) Two isochoric process and two isothermal process
(d) Two isochoric process and two isentropic process

Q3. When a liquid flow through a tube with sub-cooled or saturated boiling, what is the process known?
(a) Pool boiling
(b) Bulk boiling
(c) Convection boiling
(d) Forced convection boiling

Q4. 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

Q5. There is no work transfer involved in this process
(a) Adiabatic expansion
(b) Isothermal expansion
(c) Polytropic expansion
(d) Free expansion

Q6. In order to double the period of simple pendulum
(a) the mass of its bob should be doubled
(b) the mass of its bob should be quadrupled
(c) its length should be doubled
(d) its length should be quadrupled

Q7. Duralumin is an alloy of
(a) Vanadium
(b) Aluminium
(c) Tungsten
(d) Iron

Q8. Window AC has an expansion device named as
(a) Expansion valve
(b) Thermostatic valve
(c) Capillary tube
(d) Piston-cylinder

Q9. An object weighs 40 N in air and 30 N, when submerged in water then specific gravity of body is
(a) 4/3
(b) 3/4
(c) 4
(d) 3

Q10. A thick lubrication is
(a) a stable lubrication and there is no metal to metal contact
(b) a stable lubrication because there is some amount of metal to metal contact
(c) an unstable lubrication because there is some amount of metal to metal contact
(d) an unstable lubrication because there is no metal to metal contact

Solutions

S1. Ans (d)
Sol.
∈(fin)=√(kP/hA)
∈ ∝ K^(1/2)
∈ ∝ P^(1/2)
Thus, fin effectiveness will increase if thermal conductivity and circumference increases.

S2. Ans (b)
Sol. Ericsson Cycle consists of two constant pressure processes and two isentropic processes.

S3. Ans (b)
Sol. Pool Boiling: In this case the liquid above the hot surface is essentially stagnant and its motion near the surface is due to free convection.
Forced Convection Boiling: This refers to a situation where the fluid motion is induced by external means. This type of boiling occurs in water tube boilers involving forced convection.
Sub-Cooled or Local Boiling: In this case the liquid temperature is below the saturation temperature and bubbles are formed in the vicinity of heat surface.
Saturated Boiling: Here, the liquid temperature exceeds the saturation temperature.

S4. 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.

S5. Ans (d)
Sol. Since free expansion occurs against vacuum hence no work is done by the expanding fluid.

S6. Ans.(d)
Sol. We know that
T∝√L
T = Time period
L = Length of pendulum
In order to double the period of simple pendulum, its length should be quadrupled.

S7. Ans.(b)
Sol. Duralumin is an alloy, a trade name given to the earliest types of the age harden able aluminium alloys. It is an alloy made up of 90% aluminum,4% copper, 1% magnesium and 0.5% to 1% manganese.

S8. (c)
Sol. In window AC capillary tube is used as an expansion device as it is cost effective and simple.

S9. Ans.(c)
Sol. We know,
Buoyancy on body=weight of body in air-weight of body in water
=40-30
=10 N
specific gravity of solid body
=(density of body)/(density of standard liquid or water)
=(weight of body)/(buoyancy on body)
=40/10
=4

S10. Ans.(a)
Sol. A thick lubrication is a stable lubrication and there is no metal to metal contact.

Quiz: Mechanical Engineering 22 June 2020

Quiz: Mechanical Engineering
Exam: UPSSSC JE
Topic: Miscellaneous

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

Q1. A closed thermodynamic system is one in which
(a) there is no energy or mass transfer across the boundary
(b) there is no mass transfer, but energy transfer exists
(c) there is no energy transfer, but mass transfer exists
(d) both energy and mass transfer take place across the boundary, but the mass transfer is controlled by valves

Q2. Which one of the following represents the condensation of a mixture of saturated liquid and saturated vapour on the enthalpy-entropy diagram?
(a) A horizontal line
(b) an inclined line of constant slope
(c) A vertical line
(d) A curved line

Q3. Consider the following statements:
1. The increase in metacentric height
2. Increases stability
3. Decreases stability
4. Increases comfort for passengers in a ship
5. 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

Q4. Which one of the following is measured by a rotameter?
(a) Velocity of fluids
(b) Discharge of fluids
(c) Viscosity of fluids
(d) Rotational speed of solid shafts

Q5. When a liquid flow through a tube with sub-cooled or saturated boiling, what is the process known?
(a) Pool boiling
(b) Bulk boiling
(c) Convection boiling
(d) Forced convection boiling

Q6. The turbomachine used to circulate refrigerant in large refrigeration plant is
(a) A centrifugal compressor
(b) A radial turbine
(c) An axial compressor
(d) An axial turbine

Q7. Air at 35°C DBT and 25°C dew point temperature passes through the water shower whose temperature is maintained at 20°C. What is the process involved?
(a) cooling and humidification
(b) sensible cooling
(c) cooling and dehumidification
(d) heating and humidification

Q8. In an internally pressurized thick cylinder, the hoop stress
1. Remains constant but the radial stress varies parabolically
2. Varies parabolically but the radial stress remains constant
Which of the above is/are correct?
(a) 1 only
(b) 2 only
(c) Both 1 and 2
(d) Neither 1 nor 2

Q9. Which of the following are associated with Ackerman steering mechanism used in automobiles?
1. Has both sliding and turning pairs
2. Less friction and hence long life
3. Mechanically correct in all positions
4. Mechanically not accurate except in three positions
5. Has only turning pairs
6. Controls movement of two front wheels
(a) 2, 4, 5 and 6
(b) 1, 2, 3 and 6
(c) 2, 3, 5 and 6
(d) 1, 2, 3 and 5

Q10. In a tensile test on mild steel specimen, the breaking stress as compared to ultimate tensile stress is
(a) more
(b) less
(c) same
(d) more/less depending on composition

Solutions

S1. Ans.(b)
Sol. A closed system consists of fixed amount of mass and no mass can cross its boundary but energy in the form of heat and work can cross the boundary.

S2. Ans.(b)
Sol. For Mollier diagram, condensation takes place at constant pressure which is along vertically inclined.

S3. Ans (b)
Sol. Time period of oscillations is inversely proportional to meta centric height. Thus, more the GM less will be time period, and body regains its position in less time. So more stable.

S4. Ans.(b)
Sol. Rotameter and elbow meter measure discharge through pips

S5. Ans (b)
Sol. Pool Boiling: In this case the liquid above the hot surface is essentially stagnant and its motion near the surface is due to free convection.
Forced Convection Boiling: This refers to a situation where the fluid motion is induced by external means. This type of boiling occurs in water tube boilers involving forced convection.
Sub-Cooled or Local Boiling: In this case the liquid temperature is below the saturation temperature and bubbles are formed in the vicinity of heat surface.
Saturated Boiling: Here, the liquid temperature exceeds the saturation temperature.

S6. Ans (a)
Sol. Large amount of vapour refrigerant at low pressure is required to handle in large refrigerant plant. Also unlike reciprocating compressor, centrifugal compressor are steady-flow device hence subjected to less vibration and noise.

S7. Ans.(c)
Sol. As the temperature of water shower is less than dew point temperature hence, water vapour starts condensing. Thus, process involved is cooling and dehumidification.

S8. Ans.(d)
Sol. For thick cylinder
1. Variations of hoop stress and radial stress are parabolic across the cylinder wall.
2. at the inner edge, the stresses are maximum.
3. the value of ‘permissible or Maximum Hoop stress’ is to be considered on the inner edge,
4. the maximum shear stress (σmax) and Hoop, longitudinal and radial strains (εh,εl,εr) are calculated as in thin cylinder but separately for inner and outer edges.

S9. Ans.(a)
Sol. the following things are associated with Ackerman steering mechanism used in automobiles.
1. Less friction and hence long life
2. Mechanically correct in all positions
3. Mechanically not accurate except in three positions
4. Has only turning pairs
5. Controls movement of two front wheels

S10. Ans (b)
Sol. Ultimate stress is the maximum value of stress. It is the point at which the size (cross section area) decreases and a neck is formed, and breaking stress is the stress at which the material actually breaks down.
The value of ultimate stress is always more than the breaking stress as formation of neck (permanent deformation) requires more stress than to actually break.

Quiz: Mechanical Engineering 19 June 2020

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

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

Q1. Ultimate strength to cement is provided by
(a) Di-calcium silicate
(b) Tri-calcium silicate
(c) Tri-calcium aluminate
(d) Tetra calcium alumino ferrite

Q2. Misrun is a casting defect which occurs due to
(a) very high pouring temperature of the molten metal
(b) insufficient fluidity of the molten metal
(c) absorption of gases by the liquid metal
(d) improper alignment of the mould flask

Q3. Which of the following arc welding process does not use consumable electrode?
(a) GTAW
(b) GMAW
(c) Resistance welding
(d) SAW

Q4. In thermodynamics, pure substance is one which
(a) behaves like a perfect gas
(b) consists of only a single chemical species
(c) has no dissolved impurities
(d) has a number of chemical species but has constant composition

Q5. Entropy of mixing is
(a) Zero
(b) Positive
(c) Negative
(d) Dependent on gases dissolved

Q6. The forces being dealt with in fluid statics are
(a) Gravity forces and surface tension
(b) Gravity forces and viscous forces
(c) Gravity forces and pressure forces
(d) None of these

Q7. The printer’s ink is an example of
(a) Newtonian fluid
(b) Idea fluid
(c) Rheopectic fluid
(d) Plastic fluid

Q8. In thick film hydro-dynamic journal bearing, the coefficient of friction
(a) decreases with increase in load
(b) increases with increase in load
(c) is independent on load
(d) None of these

Q9. For a part subjected to stress reversal, which of the following section is preferred?
(a) Channel section
(b) I-section
(c) T-section
(d) Hollow cylindrical pipe

Q10. If the line of movement of the follower passes through the center of rotation of cam then it is called
(a) Axial follower
(b) Radial follower
(c) Offset follower
(d) None of these

Solutions

S1. Ans (a)
Sol. Ultimate strength to cement is provided by Di-calcium silicate.

S2. Ans (b)
Sol. Pouring metal defects include misruns, cold shuts, and inclusions. A misrun occurs when the liquid metal does not completely fill the mould cavity, leaving an unfilled portion. Both are caused by either a lack of fluidity in the molten metal or cross-sections that are too narrow.

S3. Ans (a)
Sol. Gas tungsten arc welding (GTAW) uses a non- consumable electrode to produce arc between electrode and workpiece for welding. The weld is shielded from the atmosphere by a shielding gas that forms an envelope around the weld area.

S4. Ans (d)
Sol. In thermodynamics, pure substance is one which has a number of chemical elements but composition is same throughout its volume.

S5. Ans (b)
Sol. As mixing is an internally irreversible process, so entropy of the universe will increase or change in entropy is positive.

S6. Ans (c)
Sol. Fluid statics dealt with following forces-
1.Gravity force
2.Pressure force

S7. Ans (c)
Sol. Printer’s ink is an example of Rheopectic fluid, in which viscosity of the fluid increases as the time passes.

S8. Ans (a)
Sol. In hydrodynamic journal bearing for thick film lubrication zone, when we increase load on the bearing then coefficient of friction decrease.

S9. Ans (b)
Sol. I-section will be preferred for the reversal load applications because it has the highest moment of inertia for the same volume of material.

S10. Ans (b)
Sol. If the line of movement of the follower passes through the center of rotation of cam then it is called radial follower.

Quiz: Mechanical Engineering 18 June 2020

Quiz: Mechanical Engineering
Exam: UPPSC AE
Topic: Miscellaneous

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

Q1. Availability of a system at any given stage is
(a) a property of the system
(b) the total energy of the system
(c) the minimum work obtainable as the system goes to dead state
(d) the maximum useful work obtainable as the system goes to dead state

Q2. The irreversibility associated with the process is defined as
(a) Loss of qualitative energy
(b) Loss of energy
(c) Loss of enthalpy
(d) Loss of entropy

Q3. Which one of the following methods is more effective to improve the efficiency of the Rankine cycle used in thermal power plant?
(a) Increasing the condenser temperature
(b) Decreasing the condenser temperature
(c) Decreasing the boiler temperature
(d) Increasing the boiler temperature

Q4. Air pre-heater
(a) increases evaporative capacity of a boiler
(b) increases the efficiency of boiler
(c) enables low grade fuel to be burnt
(d) all of the above

Q5. The work output of theoretical Otto cycle
(a) Increases with increase in compression ratio
(b) Increases with increase in pressure ratio
(c) Increases with increase in adiabatic index
(d) All of the above

Q6. In emission measuring equipments, the HC is measured using
(a) Gas Chromatograph
(b) Flame ionization detector
(c) Chemiluminescence detector
(d) NDIR analyser

Q7. If the pressure range of compressor is low, then the COP will be
(a) low
(b) high
(c) remains unchanged
(d) cannot be determined

Q8. Multi-evaporator systems with a single compressor and a pressure reducing valve:
(a) Yield very high COP as compared to single stage systems
(b) Yield lower compressor discharge temperature compared to single stage systems
(c) Yield slightly higher refrigeration effect in the low temperature evaporator
(d) Yield slightly high refrigeration effect in high temperature evaporator compared to single stage systems

Q9. If the ratio of emission of a body to that of a black body at a given temperature is constant for all wavelengths, the body is called:
(a) Black body
(b) Gray body
(c) White body
(d) Opaque body

Q10. Steel and cast-iron pipes carrying fluid under pressure are regarded as hydraulically smooth when
(a) the boundary surface is relatively smooth
(b) the roughness projections are of low height
(c) the roughness elements are completely covered by the laminar sub-layer
(d) the laminar layer is thin as compared to the average height of roughness element

Solutions

S1. Ans.(d)
Sol. Availability of a system at any given stage is defined as the maximum useful work obtainable as the system goes to dead state.

S2. Ans.(a)
Sol. The loss of qualitative energy or degradation of energy is associated with the irreversibility of the system.

S3. Ans.(b)
Sol. There are following methods to increase the efficiency of Rankine cycle:
1. Lowering the condenser pressure
2. Super-heating the steam to high temperature
3. Increasing the boiler pressure

S4. Ans.(d)
Sol. Air preheater has following effects in a power plant
1.Increases in evaporative capacity of a boiler
2.Increases the efficiency of boiler
3.Enables low grade fuel burning

S5. Ans.(d)
Sol. Work output of Otto cycle increases with pressure ratio, compression ratio and adiabatic index.

S6. Ans.(b)
Sol. HC is measured with the help of flame ionization detector. The flame ionization detector passes sample and carrier gas from the column through a hydrogen-air flame. The hydrogen-air flame alone creates few ions, but when an organic compound is burned there is an increase in ions produced. A polarizing voltage attracts these ions to a collector located near the flame.

S7. Ans.(b)
Sol. If pressure range is low then the compressor work done will be low and hence, COP will be high.

S8. Ans.(d)
Sol. Multi-evaporator system with a single compressor and a pressure reducing valve yield slightly higher refrigeration effect in the high temperature evaporator compared to single stage systems.

S9. Ans.(b)
Sol. If the ratio of emission of a body to that of a black body at a given temperature is constant for all wavelengths, the body is called Gray body.

S10. Ans.(c)
Sol. When the thickness of laminar sub-layer is more than the average height of roughness then it is called hydraulically smooth surface.

Quiz: Mechanical Engineering 16 June 2020

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

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

Q1. Permanent deformation of solid material under the influence of long-term exposure of high level of mechanical stresses that are still below the yield strength along with subjected to heat is……..
(a) Elasticity
(b) Isotropy
(c) Hardness
(d) Creep

Q2. The weld bead between a heavy steel section and a thin section occurs mainly due to the formation of:
(a) Bainite
(b) Spheroidite
(c) Martensite
(d) None of these

Q3. A solid and a liquid result in a liquid upon heating during _________ reaction.
(a) Eutectic
(b) Peritectic
(c) Monotectic
(d) Syntectic

Q4. Titanium in the steel improves the
(a) hardness
(b) strength
(c) resistance to corrosion of steel
(d) strength and resistance to corrosion of steel

Q5. In the casting, ‘’Bell’’ shape products are generally made by
(a) Single piece pattern
(b) Gated pattern
(c) Cope and drag pattern
(d) Sweep pattern

Q6. In straight polarity welding-
(a) electrode holder is connected to the negative and the work to positive lead
(b) electrode holder is connected to the positive and the work to negative lead
(c) electrode holder to be earthed and work to positive head
(d) electrode holder is connected to the negative lead and the work to be earthed

Q7. The value of side rake angle of the turning tool having tool signature:
0°,10°,8°,6°,20°,60°,0.01(mm) will be:
(a) 60°
(b) 20°
(c) 10°
(d) 8°

Q8. No liquid can exist as a liquid at
(a) 0 Deg C temperature
(b) 200 Deg C temperature
(c) Zero pressure
(d) Zero viscosity

Q9. A shock wave is produced when
(a) a sonic flow changes to supersonic flow
(b) a subsonic flow changes to sonic flow
(c) a supersonic flow changes to subsonic flow
(d) none of these

Q10. Consider the following statements regarding the ends of the pressure vessels flanged by pre-tensioned bolts:
1. Pre-tensioning helps to seal the pressure vessel.
2. Pre-tensioning reduces the maximum tensile stress in the bolts
3. Pre-tensioning increases the fatigue life of the bolts.
Which of the above statements are correct?
(a) 1 and 2
(b) 2 and 3
(c) 1 and 3
(d) 1,2 and 3

Solutions

S1. Ans (d)
Sol. Permanent deformation of solid material under the influence of long-term exposure of high level of mechanical stresses that are still below the yield strength along with subjected to heat is known as creep.

S2. Ans (a)
Sol. The weld bead between a heavy steel section and a thin section occurs mainly due to the formation of bainite.
Bainite is formed by isothermal decomposition of Austenite in alloy steels.

S3. Ans (c)
Sol. A solid and a liquid result in a liquid after heating during monotectic reaction.
i.e. Solid 1 + Liquid 1⇌Liquid 2

S4. Ans (d)
Sol. Titanium in the steel improves following properties-
1.Strength
2.Corrosion resistance

S5. Ans (d)
Sol. Sweep pattern is used for the casting of ‘’Bell’’ shaped or 3D symmetrical object.

S6. Ans (a)
Sol. In straight polarity welding, electrode is made negative and work-piece is made positive. Straight polarity welding increases penetration in welding.

S7. Ans (c)
Sol. We know that American standard association (ASA) tool signature has following sequence.
1.Back rake angle- 0°
2.Side rake angle- 10°
3.End relief angle- 8°
4.Side relief angle- 6°
5.End cutting edge angle- 20°
6.Side cutting edge angle- 60°
7.Nose radius- 0.01 mm

S8. Ans (c)
Sol. No liquid can exist as a liquid at zero pressure because at zero pressure, molecular momentum of the liquid becomes very high and if liquid taken to zero pressure which effectively means vacuum, in that case, it will boil and vaporize.

S9. Ans (c)
Sol. A shock wave is a type of propagating disturbance that moves faster than the local speed of sound in a medium. Shock wave is produced when a supersonic flow changes to subsonic flow.

S10. Ans (c)
Sol. Pre-tensioning increases fatigue life of the bolt, maximum tensile stress in the bolt and helps to seal the pressure vessel.

Quiz:Mechanical Engineering 15 June 2020

Quiz: Mechanical Engineering
Exam: UPSSSC JE
Topic: Miscellaneous

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

Q1. In a reaction stage turbine, the velocity
(a) increases in stator and remains constant in rotor
(b) increases in stator and decreases in rotor
(c) decreases in stator and remains constant in rotor
(d) remains constant throughout

Q2. With Reheat Rankine cycle:
(a) Quality of exhaust steam is improved
(b) Network output of cycle increases
(c) Specific steam consumption decreases
(d) All of the above

Q3. The knocking sensitivity of S.I. engines could be reduced by:
(a) Compact combustion chamber geometry
(b) Central position of the spark plug
(c) Increased turbulence
(d) All of the above

Q4. Which device can be used to measure aromatic hydrocarbon in exhaust gas?
(a) Dispersion analyser
(b) Non-dispersive infrared analyser
(c) Flame ionization detector
(d) All of the above

Q5. Which of the following is not true for heat pump?
(a) Low temperature reservoir is environment
(b) Low temperature reservoir is conditioned space
(c) It is a cyclic device
(d) Work done is negative

Q6. Amongst the following options what remains constant during adiabatic saturation process on unsaturated air?
(a) Dew point temperature
(b) Relative humidity
(c) Wet bulb temperature
(d) Dry bulb temperature

Q7. A stone weighs 405 N in air and 206 N in water. Find the weight of water displaced.
(a) 206
(b) 199
(c) 200
(d) 405

Q8. Temperature stresses are set up in a material when
(a) It is free to expand or contract
(b) It is first heated then cooled
(c) It is first cooled and then heated
(d) Its expansion and contraction are restrained

Q9. A transmission shaft includes:
(a) Counter shaft
(b) Line shaft
(c) Over head shaft
(d) All of these

Q10. The unbalanced force due to reciprocating masses
(a) Varies in magnitude but constant in direction
(b) Varies in direction but constant in magnitude
(c) Varies in both magnitude and direction
(d) Constant in both direction and magnitude

Solutions

S1. Ans (b)
Sol. In a reaction stage turbine, the velocity increases in stator as it works as a nozzle and decreases in rotor.

S2. Ans (d)
Sol. With Reheat application in Rankine cycle,
1.Work output increases
2.Dryness fraction or quality of steam improves
3.Specific steam consumption i.e. Steam consumption per KWh decreases due to increases in work output

S3. Ans (d)
Sol. Knocking sensitivity in S.I. engine can be reduced by:
1.Compact construction of combustion chamber to reduce flame travel distance
2.Locating the spark plug centrally or near exhaust valve
3.Increasing turbulence

S4. Ans (d)
Sol. An aromatic hydrocarbon or arene (or sometimes aryl hydrocarbon) is a hydrocarbon with sigma bonds and delocalized pi electrons between carbon atoms forming a circle.
Dispersion analyser, Non-dispersive infrared analyser and flame-ionization detector all are used for measure aromatic hydrocarbon in exhaust gases.

S5. Ans (b)
Sol. Heat pump is a cyclic device, in which high temperature reservoir is a conditioned space maintained above the temperature of surrounding. Work done is negative for the heat pump.

S6. Ans (c)
Sol. Adiabatic saturation process is that process in which water converts into vapour and mixed with air till its saturation, adiabatically.
Wet bulb temperature remains constant during this process.

S7. Ans (b)
Sol. According to Archimedes principle,
Weight of displaced water = weight of stone in air-weight of stone in water
=405-206=199 N

S8. Ans (d)
Sol. When there is generation of thermal strain (tensile or compressive) in a body due to change in temperature and it is made restricted for this, then stresses (tensile or compressive depending upon the temperature decrease or increase) will be generated in it.

S9. Ans (d)
Sol. A power transmission can be done by using counter shaft, line shaft and overhead shaft etc.

S10. Ans (a)
Sol. The unbalanced force due to reciprocating masses has same direction irrespective of the magnitude but magnitude may change.

Quiz:Mechanical Engineering 12 June 2020

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

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

Q1. If maximum surface temperature of sea is 30 Deg C and temperature in depth is 4 Deg C, how much can be the maximum thermal efficiency of Ocean Thermal Conversion (OTEC) System?
(a) 8.58%
(b) 13.3%
(c) 86.7%
(d) None of these

Q2. Critical pressure of a liquid is the pressure
(a) above which liquid will remain liquid
(b) above which liquid will become gas
(c) above which liquid becomes vapour
(d) above which liquid becomes solid

Q3. In binary vapour cycle
(a) Mercury is used in the bottoming cycle
(b) Steam is used in topping cycle
(c) Mercury is used in topping cycle
(d) Either mercury or steam is used in topping cycle

Q4. In fire tube boilers, pressure is limited to
(a) 16 bar
(b) 32 bar
(c) 48 bar
(d) 64 bar

Q5. The efficiency of Diesel cycle approaches to Otto cycle efficiency when
(a) cut-off is increased
(b) cut-off is decreased
(c) cut-off is zero
(d) cut-off is constant

Q6. In a low speed S.I. engine, the inlet valve closes approximately:
(a) 40° after BDC
(b) 30° before BDC
(c) 10° after BDC
(d) 10° before BDC

Q7. The main characteristic feature of Air Refrigeration System is
(a) High COP
(b) throughout the cycle the refrigerant remains in gaseous state
(c) Weight of air circulate is less
(d) High refrigerating cost

Q8. Saturation temperature of the water vapour in the moist air is known as:
(a) Dry bulb temperature
(b) Dew point temperature
(c) Wet bulb temperature
(d) Critical temperature

Q9. A thermocouple responds well when
(a) its coefficient of heat transfer is high
(b) its probe diameter is less
(c) its density is more
(d) its specific heat is more

Q10. If Buoyancy force is 30000 N on a body and viscous force is 3 N, then considering natural convection, what is the value of Grashoff number?
(a) 10000
(b) 1000
(c) 0.0001
(d) 100

Solutions

S1. Ans (a)
Sol. We know that
η=(T1-T2)/T1
=(30-4)/303=8.58%

S2. Ans (c)
Sol. Critical pressure is that pressure above which boundary difference between liquid and vapor vanishes.

S3. Ans (c)
Sol. In the binary vapour cycle, mercury is used in topping cycle because of the physical and thermodynamic properties of the mercury working fluid, require a heat source that operates in the temperature range of about 535°C to 700°C.

S4. Ans (a)
Sol. Fire tube boiler are the low-pressure boilers, they operate below a pressure of 20 bar. E.g. Cochran, Lancashire, Locomotive boilers etc.

S5. Ans (c)
Sol. Cut-off ratio is the ratio of volume of charge at which heat addition stops and swept volume. When cut-off ratio (ρ) is zero then the efficiency of diesel cycle approaches to that of Otto cycle.

S6. Ans (c)
Sol. In a low speed S.I. engine, the inlet valve closes approximately 10° after BDC because inertia of the charge is low which reduces volumetric efficiency. To maintain volumetric efficiency, we make the inlet valve to close 10° after BDC.

S7. Ans (b)
Sol. Air refrigeration cycle works on the reverse Brayton cycle. The main characteristic feature of Air Refrigeration System is throughout the cycle the refrigerant remains in gaseous state.

S8. Ans (b)
Sol. The temperature of water vapour at which air becomes saturated is called dew point temperature.

S9. Ans (a)
Sol. Time constant =ρvc/(hoA)
As, time constant decreases then thermocouple responds quickly. For decreasing this value, we have to increase heat transfer coefficient (ho).

S10. Ans (a)
Sol. We know that
Grashoff number=(Buoyancy force)/(Viscous force)
Gr=30000/3=10000

Quiz:Mechanical Engineering 11 June 2020

Quiz: Mechanical Engineering
Exam: UPPSC AE
Topic: Manufacturing Engineering

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

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

Q2. Ability of a material to exhibit considerable elastic recovery on release of load, is known as:
(a) Toughness
(b) Stiffness
(c) Resilience
(d) Hardness

Q3. Martensite is a supersaturated solution of carbon in:
(a) Alpha iron
(b) Beta iron
(c) Gamma iron
(d) Delta iron

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

Q5. Chills are:
(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. In an Oxy-acetylene welding, the ratio of oxygen to acetylene in reducing flame is
(a) 0.5: 1
(b) 1: 3.1
(c) 1: 1.2
(d) 1: 1

Q7. The merchant circle is used to
(a) Improve the quality of a product
(b) Find the principal stress and principal strain
(c) Fix the price of a product in the market
(d) Establish the shear angle relationship in machining

Q8. Oblique cutting system is also known as:
(a) One-dimensional cutting system
(b) Two-dimensional cutting system
(c) Three-dimensional cutting system
(d) None of these

Q9. Which of the following lathes is suitable for a small engineering workshop involved in repair work?
(a) Center lathe
(b) Tool-room lathe
(c) Special purpose lathe
(d) Capstan lathe

Q10. It is desired to perform the operations like drilling, reaming, counter-boring etc. on a work-piece. Which of the following machines will be used?
(a) Sensitive drilling machine
(b) Radial drilling machine
(c) Gang drilling machine
(d) Multiple spindle drilling machine

Solutions

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

S2. Ans.(c)
Sol. Resilience is the ability of the material to exhibit considerable elastic recovery on release of load.

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

S4. Ans.(a)
Sol. Chromium has Body-centered Cubic structure at room temperature. BCC structure has 2 atoms in a unit cell.

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.(b)
Sol.
1) Neutral flame
Ratio of O2 /C2H2 is 1:1 =2.5 mole oxygen/1 mole C2H2
=31.99×2.5/ 26.037×1
= 3.071:1
2) Carburizing flame
Ratio less than 3.071:1
3) Oxidizing flame
Ratio more than 3.071:1

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.(c)
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.(a)
Sol. For small engineering workshops, which are involved in repair works; center lathe is suitable. The main common tasks that can be performed on center lathe:
1.Facing
2.Turning
3.Drilling
4.Boring
5.Threading
6.Knurling
7. Chamfering

S10. Ans.(c)
Sol. When we place a number of single spindle drilling machine columns together on a common work-table, then the machine is called gang drilling machine.

Quiz:Mechanical Engineering 9 June 2020

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

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

Q1. For a given set of operating pressure limits of a Rankine cycle the highest efficiency occurs for
(a) Saturated cycle
(b) Superheated cycle
(c) Reheat cycle
(d) Regenerative cycle

Q2. High API gravity of fuel means:
(a) Lower Diesel index
(b) Lower Brake specific fuel consumption
(c) Lower heat of combustion
(d) Lower ignition quality

Q3. A refrigerant should have:
(a) High specific heat of liquid
(b) High boiling point
(c) High latent heat of vaporization
(d) Low critical temperature

Q4. Lumped heat capacity approach of transient heat conduction analysis is used:
(a) For bodies of very high conductive resistance
(b) When temperature variation throughout the body is very high
(c) When temperature variation throughout the body is very low
(d) For Biot number > 10

Q5. What happens to the liquid level, when a small diameter tube is inserted into a liquid whose contact angle is 125°?
(a) Liquid level in the tube will fall first and then rise.
(b) Liquid level in the tube falls.
(c) Liquid level in the tube remains constant
(d) Liquid level in the tube rises

Q6. A Rotameter can be used
(a) Only in vertical orientation (direction)
(b) Only in horizontal orientation (direction)
(c) In any orientation (direction)
(d) For zero orientation (direction)

Q7. Two simply supported beams of equal lengths, cross sectional areas and section moduli, are subjected to the same concentrated load at its mid-length. One beam is made of steel and other is made of Aluminium. The maximum bending stress induced will be in
(a) Steel beam
(b) Aluminium beam
(c) Both beams of equal magnitude
(d) The beams according to their Elastic moduli magnitude

Q8. In clamp coupling, power is transmitted by means of-
(a) Friction force
(b) Shear resistance
(c) Crushing resistance
(d) Tear resistance

Q9. The primary cause for deflection of arc during arc welding is………..
(a) Hydro static field
(b) Magnetic field
(c) Explosive field
(d) Wind velocity field

Q10. A bearing material should not possess the characteristic of high…………
(a) coefficient of friction
(b) hardness
(c) melting point
(d) thermal conductivity

Solutions

S1. Ans (d)
Sol. For given operating pressure limits in a Rankine cycle, the highest efficiency occurs for Regenerative cycle. It is because mean temperature of heat addition increases in the regenerative cycle.

S2. Ans (b)
Sol. API stands for American Petroleum institute. API gravity is a measure of how heavy or light a petroleum liquid is as compared to water. High API gravity of fuel represents lower brake specific fuel consumption.

S3. Ans (c)
Sol. There are following properties of a good refrigerant:
1.Low boiling point.
2.Low freezing point
3.High latent heat of vaporization
4.Low viscosity
5.Low specific volume
6.High critical temperature

S4. Ans (c)
Sol. Lumped heat capacity approach of transient heat conduction analysis is used when conductive resistance of the body is negligible and hence, the variation in temperature throughout the body is also negligible.

S5. Ans (b)
Sol. When angle of contact is more than 90°, then liquid level will fall in the tube. In contradiction, when angle of contact is less than 90°, then liquid level will rise in the tube.

S6. Ans (a)
Sol. A Rotameter is a device that measures the volumetric flow rate of a fluid in a closed tube. It can be used in only vertical orientation.

S7. Ans (c)
Sol. We know that bending-moment equation,
M/I=σ/y
σ=My/I
Since, maximum bending moment and section modulus of both the beams are same, then maximum bending stress induced in both the beams will be same.

S8. Ans (a)
Sol. The main mean of power transmission in clamp coupling is frictional force.

S9. Ans (b)
Sol. The primary cause for deflection of arc, during arc welding is magnetic field called arc blow. Arc blow is mainly, the deflection of electric arc from its regular path.

S10. Ans (a)
Sol. A good bearing material should possess following properties:
1.Low coefficient of friction.
2.High hardness
3.High melting point
4.High thermal conductivity

 

 

 

 

 

 

 

Quiz: Mechanical Engineering 8 June 2020

Quiz: Mechanical Engineering
Exam: UPSSSC JE
Topic: Miscellaneous

Each question carries 1 mark
Negative marking: 1/3 mark
Time: 10 Minutes
Q1. A metal block is thrown into deep lake. As it sinks deeper in water, the buoyant force acting on it
(a) increases
(b) remains the same
(c) decreases
(d) first increases and then decreases

Q2. Which of the following statements is wrong?
(a) Streamlines cannot start or end anywhere except at the interface or infinity.
(b) Streamline spacing varies directly as the flow velocity.
(c) Streamlines can meet at a stagnation point where the velocity is zero.
(d) The flow is only along the streamline and not across it.

Q3. In a Carnot engine, when working substance gives heat to the sink
(a) temperature of the sink increases
(b) temperature of the sink remains same
(c) temperature of the source decreases
(d) temperature of both the sink and source decreases

Q4. Three engines A, B and C operating on Carnot cycle respectively use air, Nitrogen and Argon as the working fluid. If all the engine operates within the same temperature limit, then which engine will have highest efficiency.
(a) Engine A
(b) Engine B
(c) Engine C
(d) All engines will have same efficiency

Q5. When a system is in equilibrium, any conceivable change in entropy would be
(a) maximum
(b) zero
(c) positive
(d) negative

Q6. Which of the following is false statements?
Some of the methods used to reduce diesel smoke are as follows
(a) using additives in the fuel
(b) engine derating i.e. reducing the maximum flow of fuel
(c) increasing the compression ratio
(d) avoidance of overloading

Q7. The instrument preferred in the measurement of highly fluctuating velocities in air flows is
(a) Pitot-static tube
(b) Propeller type anemometer
(c) Three cup anemometer
(d) Hot wire anemometer

Q8. Perpetual motion machine of second kind violates the
(a) First law of thermodynamics
(b) Kelvin-Planck statement
(c) Clausius statement
(d) Third law of thermodynamics

Q9. Second law of thermodynamics defines
(a) Heat
(b) Work
(c) Enthalpy
(d) Entropy

Q10. Consider the following statements pertaining to large heat transfer rate using fins
1. Fins should be used on the side where heat transfer coefficient is small.
2. Long and thick fins should be used.
3. Short and thin fins should be used.
4. Thermal conductivity of fin material should be large.
Which of the above statements are correct?
(a) 1, 2 and 3
(b) 1, 2 and 4
(c) 2, 3 and 4
(d) 1, 3 and 4

SOLUTION

S1. Ans (b)
Sol. As buoyant force depends only on the displaced volume of fluid by the submerged or floating body according to Archimedes principle. So, volume displaced by the metal block will remain constant from when it sinks in the fluid till it sinks deeper, hence, the buoyant force on the metal block remains same.

S2. Ans (b)
Sol. Streamline spacing is inversely proportional to the velocity, it means for accelerated flow spacing between streamlines is less and for retarded flow, this spacing will be more.

S3. Ans (b)
Sol. When working substance gives heat to the sink then its temperature remains same
because sink and source both are considered as reservoir of heat.

S4. Ans (d)
Sol. As efficiencies of Carnot engines working between same temperature limits do not depend upon working fluid of engines.
So, engine A, B and C all three will have same efficiency.

S5. Ans (b)
Sol. When a system is in equilibrium, any conceivable change in entropy would be zero.
Because when a system reaches in equilibrium state then its entropy will be maximum at that state.

S6. Ans (c)
Sol. Increasing the compression ratio is not recommended to reduce diesel smoke as it increases the weight of the engine and cost which is not worthy for reducing diesel smoke.

S7. Ans (d)
Sol. Hot wire anemometer is used for the measurement of highly fluctuating velocities in air. This can be done by measuring the heat loss of the wire which is placed in the fluid stream. The wire is heated by electrical current. The hot wire when placed in the stream of the fluid, in that case, the heat is transferred from wire to fluid, and hence the temperature of wire reduces. The resistance of wire measures the flow rate of the fluid which is the function of heat loss from the wire and change in the resistance of wire.

S8. Ans (b)
Sol. Perpetual motion machine of the second kind is a machine which produces work while exchanging heat from a single heat source. Which violates Kelvin-Planck statement of Second law of thermodynamics.

S9. Ans (d)
Sol. Second law of thermodynamics defines Entropy or energy degradation.
As second law of thermodynamics states that Heat (low grade energy) cannot be converted into work (high grade energy) completely because it violates Kelvin-Planck statement.

S10. Ans (d)
Sol. Fins are used where thermal conductivity of material is high and coefficient of heat transfer is small. We should use short and thin fins to increase heat transfer area exposed to environment.

Quiz: Mechanical Engineering 05 June 2020

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

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

Q1. Critical speed of a turbine is
(a) Same as runaway speed
(b) Speed that will cause mechanical failure of the shaft
(c) Speed at which natural frequency of vibrations equals the number of revolutions at the same time
(d) Speed equal to synchronous speed of the generator

Q2. A single fixed-point temperature scale is based on
(a) ice point
(b) steam point
(c) triple point of water
(d) critical point of water

Q3. When the fluid flows over the flat plate with a sharp leading edge is examined, laminar flow is generally observed for Reynolds number less than
(a) 2300
(b) 1500
(c) 5×10^5
(d) 1000

Q4. A floating body will be in unstable equilibrium
(a) when its metacentric height is zero
(b) when the metacentre is above center of gravity
(c) when the metacentre is below center of gravity
(d) when the metacentre is at center of gravity

Q5. Mach number is defined as the square root of the ratio of the
(a) inertia force to the pressure force
(b) inertia force to the elastic force
(c) inertia force to the surface tension force
(d) none of these

Q6. The force applied on a body of mass 100 kg to produce an acceleration of 5 m/s^2 is
(a) 500 N
(b) 100 N
(c) 20 N
(d) 10 N

Q7. In case of a circular shaft subjected to torque, the value of shear stress
(a) is uniform through out
(b) has maximum value at axis
(c) has maximum value at the surface
(d) is zero at the axis and linearly increases to a maximum value at the surface of a shaft

Q8. A ball bearing designated by the number 408 is a:
(a) Extra light bearing
(b) Light bearing
(c) Medium bearing
(d) Heavy bearing

Q9. Y-alloy is an alloy of
(a) Nickel
(b) Aluminium
(c) Copper
(d) Tin

Q10. The ultimate tensile strength of low carbon steel by working at high strain rate will
(a) increase
(b) decrease
(c) remain constant
(d) first increase, then decrease

Solutions

S1. Ans (c)
Sol. Critical speed of a turbine is the speed of revolutions which is equal to natural frequency of vibration.

S2. Ans (c)
Sol. A single fixed-point temperature scale is based on triple point of water. Triple point of water is that point on P-T diagram at which solid, liquid and vapour phases co-exist together.

S3. Ans (c)
Sol. Flow on a flat plate,
Reynolds number < 5×10^5 (Laminar flow)
Reynolds number > 5×10^5 (Turbulent flow)

S4. Ans (c)
Sol. Metacentric height (distance between metacentre, M and center of gravity, G) decides the stability of a floating body.
If GM > 0 then (Stable)
If GM = 0 then (Neutral)
If GM < 0 then (Unstable)

S5. Ans (b)
Sol. Mach number =√((Inertia Force)/(Elastic Force))
This is applicable for compressible flow.

S6. Ans (a)
Sol. According to Newton’s Second law
F=m.a ………………(1)
Given,
m=100 kg
a=5 m/s^2
From equation (1)
F=100×5
F=500 N

S7. Ans (d)
Sol. When a circular shaft is subjected to torsion then the shear stress will vary according to the following Torsion equation-
T/J=τ/r
τ∝r
So, shear force is zero at the axis and linearly increases to a maximum value at the surface of the shaft.

S8. Ans (d)
Sol. There are following mainly four series of bearings:
1. Extra light (100)
2. Light (200)
3. Medium (300)
4. Heavy (400)
A bearing designated with number 408 then it is used for heavy purposes. This bearing has a bore of 40 mm.

S9. Ans (b)
Sol. Y-alloy is an alloy of aluminium. Other constituents of this alloy are Copper (4%), Nickel (2%), Magnesium (1.5%), Silicon (0.5%) and Iron (0.5%) etc.

S10. Ans (a)
Sol. Ultimate tensile strength of low carbon steel increases when it is worked upon with high strain rate due to increase in number of dislocations in the material.