Quiz: Mechanical Engineering 23 July 2020

Quiz: Mechanical Engineering
Exam: UPPSC AE
Topic: Miscellaneous

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

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

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

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

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

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

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

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

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

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

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

Solutions

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

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

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

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

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

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

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

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

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

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

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