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 26 May 2020

Quiz: Mechanical Engineering
Exam: ISRO TECHNICAL ASSISTANT
Topic: Miscellaneous

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

Q1. Autofrettage is a method of
(a) joining thick cylinders
(b) Reliving stresses from thick cylinders
(c) Prestressing thick cylinders
(d) Increasing the life of thick cylinders

Q2. 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

Q3. A governor is said to be isochronous when the equilibrium speed is
(a) variable for different radii of rotation of governor balls
(b) constant for all radii of rotation of the balls within the working range
(c) constant for particular radii of rotation of governor balls
(d) constant for only one radius of rotation of governor balls

Q4. The effect of increasing the stiffness of springs of centrifugal clutch is
(a) The decrease of engagement speed
(b) The increase of engagement speed
(c) The increase of frictional force at maximum speed
(d) None of the above

Q5. The saturation temperature of steam with increase in pressure increase
(a) linearly
(b) rapidly first and then slowly
(c) slowly first and then rapidly
(d) inversely

Q6. Carbonization of coal is the process of
(a) pulverizing coal in inert atmosphere
(b) heating wood in a limited supply of air at temperatures below 300°C
(c) strongly heating coal continuously for about 48 hours in the absence of air in a
closed vessel
(d) binding the pulverized coal into brackets

Q7. Superheating of steam is done at
(a) constant volume
(b) constant temperature
(c) constant pressure
(d) constant entropy

Q8. Fluid is a substance that
(a) cannot be subjected to shear forces
(b) always expands until it fills any container
(c) has the same shear stress at a point regardless of its motion
(d) cannot remain at rest under action of any shear force.

Q9. Match List-I with List-II and select the correct answer using the code given below the lists:
List – I
Heat exchangers
Turbulent flow
Free convection
Radiation heat transfer
List–II
View factor
Effectiveness
Nusselt number
Eddy diffusivity
Codes
A B C D
(a) 3 1 2 4
(b) 2 4 3 1
(c) 3 4 2 1
(d) 2 1 3 4

Q10. Specific speed of a fluid machine
(a) refers to the speed of a machine of unit dimensions
(b) is a type-number representative of its performance
(c) is specific to the particular machine
(d) depends only upon the head under which the machine operates

SOLUTIONS

S1. Ans.(c)
Sol. Autofrettage: It is one of the oldest methods of prestressing (method of increasing pressure capacity) the cylinders. It is overloading the cylinder before it is put into service. In this method, a forged cylinder is subjected to a large internal pressure, so as to expand the internal diameter, causing overstrain. The internal pressure is applied is such a way that a portion of the cylinder at the inner surface is subjected to stresses in the plastic range. When the pressure is released, the portion of the cylinder at the outer surface contracts exerting the pressure on the portion at the inner surface which has undergone permanent deformation. As a result residual compressive stresses are induced at the inner surface and tensile stresses at the outer surface.
It is commonly used to gun barrels. It not only increases the pressure capacity of the cylinder, but also improves the endurance strength.

S2. 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.

S3. Ans.(b)
Sol. Isochronous governor is a governor that keeps the speed of a prime mover constant at all loads. Also known as a static governor. A governor is said to be isochronous if equilibrium speed is constant for all the radii of rotation in the working range. Therefore, for an isochronous governor the speed range is zero and this type of governor shall maintain constant speed.

S4. Ans.(b)
Sol. When the load is released from clutch lever, it again engages with the shaft. As the stiffness of spring will increases, the restoring force on clutch will increase and hence velocity of engagement will be more.

S5. Ans (b)
Sol. At atmospheric pressure the saturation temperature is 100°C. However, if the pressure is increased, this will allow the addition of more heat and an increase in temperature without a change of phase. Therefore, increasing the pressure effectively increases both the enthalpy of water, and the saturation temperature.

S6. Ans (c)
Sol. Coal carbonization is used for processing of coal to produce coke using metallurgical grade coal. Coal carbonization involves heating of coal in the absence of air.

S7. Ans (c)
Sol. Superheated steam is a steam at a temperature higher than its vaporization (boiling) point at the absolute pressure where the temperature is measured

S8. Ans (d)
Sol. A fluid is a substance that continuously deforms under an applied shear force.

S9. Ans.(b)
Sol.
(a) Heat exchangers : Effectiveness
(b) Turbulent flow : Eddy diffusivity
(c) Free convection : Nusselt number
(d) Radiation heat transfer : View factor

S10. Ans (b)
Sol. Specific speed is of a fluid machine is a type number representative of its performance.
In order to compare the performance of different pumps, it is necessary to have some term which will be common to all the centrifugal pump the term ordinarily used for this purpose is the specific speed. This is a type characteristic and can be used to predict the behavior of one pump based on tests of similar, but different sized pumps.
The specific speed is a characteristic of pumps which can be used as basis for comparison of the performance of different pump.

Quiz: Mechanical Engineering 22 May 2020

Quiz: Mechanical Engineering
Exam: NLC GET
Topic: Miscellaneous
Each question carries 1 mark
Negative marking: 1/3 mark
Time: 10 Minutes

Q1. The maximum force which acts on the connecting rod is
(a) Force due to gas pressure
(b) Force due to inertia of piston
(c) Force due to friction of connecting rod
(d) Force due to crank pin

Q2. Strain rosettes are generally used for
(a) measurement of load
(b) measurement of shear strain
(c) measurement of longitudinal strain
(d) measurement of resilience

Q3. Toggle mechanism have following applications except
(a) Stone crushers
(b) Gear cutting
(c) Embossing presses
(d) Switches

Q4. Match the following List-I and List-II and select the correct answer using the codes
given below the lists:
List-I
A. Pantograph
B. Single slider crank chain
C. Double slider crank chain
D. Straight line motion
List-II
1. Scotch yoke mechanism
2. Double lever mechanism
3. Tchebicheff mechanism
4. Double crank mechanism
5. Hand pump
Codes:
A B C D
(a) 4 3 5 1
(b) 2 5 1 3
(c) 2 1 5 3
(d) 4 5 2 1

Q5. The delay period in CI engine depends upon
1. Temperature and pressure in the cylinder at the time of injection
2. Strength of fuel mixture
3. Relative velocity between the fuel injection and air turbulence pressure of residual gas
4. Engine output
Select the correct answer:
(a) 1, 2, 3 and 4
(b) 1, 2 and 3
(c) 1, 2 and 4
(d) 1, 3 and 4

Q6. At breakeven point:
(a) Sales revenue > total cost
(b) Sales revenue = total cost
(c) Sales revenue < total cost
(d) None of the above

Q7. In which of the following process, a small-diameter thick ring is expanded into a large diameter thinner ring by placing the ring between two rolls
(a) Shape rolling
(b) Tube rolling
(c) Ring rolling
(d) Continuous rolling

Q8. 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

Q9. 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

Q10. Match the following List-I with List-II and select the correct answer using the codes given below
List-I
A. Rigid coupling
B. Oldham’s coupling
C. Universal joint
D. Gear coupling
List-II
1. Permits greater torque capacity for a given size
2. Permits substantial angular misalignment of intersecting axes
3. Permits substantial lateral offset and little angular alignment
4. Permits almost no misalignment
Codes:
A B C D
(a) 1 2 3 4
(b) 4 2 3 1
(c) 1 3 2 4
(d) 4 3 2 1

 

SOLUTIONS

S1. Ans (a)
Sol. All of the given forces act on the connecting rod but the major force that acts on the connecting rod is the force due to gas pressure.

S2. Ans(c)
Sol. strain rosettes are generally used for measurement of longitudinal strain.
A strain gauge rosette is a term for an arrangement of two or more strain gauges that are positioned closely to measure strains along different directions of the component under evaluation. Single strain gauges can only measure strain effectively in one direction, so the use of multiple strain gauges enables more measurements to be taken, providing a more precise evaluation of strain on the surface being measured.

S3. Ans (b)
Sol. Stone crushers, embossing presses and switches works on toggle mechanism. Mechanical advantage of toggle mechanism is infinite or very large.

S4. Ans (b)
Sol. Pantograph utilizes double lever mechanism, Hand pump utilizes single slider crank chain, Scotch-yoke mechanism is an inversion of double slider crank chain and Tchebicheff mechanism is an approximate straight-line motion mechanism.

S5. Ans (a)
Sol. Following factors affects the delay period in CI engine
1. Temperature and pressure in cylinder
2. Engine output
3. Relative velocity of fuel injection and air turbulence
4. Strength of fuel mixture
5. Compression ratio

S6. Ans(b)
Sol. Breakeven point- The breakeven point is the level of production at which the costs of production equal the revenues for a product. At breakeven point, profit will be zero even there is no loss.
Which means sales revenue is equal to total cost.
Sales revenue = total cost

S7. Ans.(c)
Sol. Ring rolling is an operation of metal forming in which a small diameter, thick ring is
converted into large diameter, thinner ring by placing the ring between two rolls.

S8. 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.

S9. 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.

S10. Ans (d)
Sol.
• Rigid coupling permits almost no misalignment.
• Oldham’s coupling permits substantial lateral offset and little angular alignment.
• Universal joint permits substantial angular misalignment of intersecting axes.
• Gear coupling permits greater torque capacity for a given size.