# Quiz: Mechanical Engineering 27 March 2020

Quiz: Mechanical Engineering
Exam: NLC GET
Topic: Miscellaneous

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

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
L1Difficulty 3
QTags Mechanical
QCereator Paper Maker 10

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
L1Difficulty 3
QTags Mechanical
QCereator Paper Maker 10

Q3. A house-top water tank is made of flat plates and is full to the brim. Its height is twice that of any side. The ratio of total thrust force on the bottom of the tank to that on any side will be:
(a) 4
(b) 2
(c) 1
(d) 0.5
L1Difficulty 3
QTags Mechanical
QCereator Paper Maker 10

Q4. In reaction turbines, the draft tube is used
(a) for the safety of the turbine
(b) to convert the kinetic energy of flow by a gradual expansion of the flow cross-section
(c) to destroy the undesirable eddies
(d) for none of the above purposes
L1Difficulty 3
QTags Mechanical
QCereator Paper Maker 10

Q5. A hydraulic press has a ram of 20 cm diameter and a plunger of 5 cm diameter. The force required at the plunger to lift a weight of 16×10^4 N shall be
(a) 256×10^4 N
(b) 64×10^4 N
(c) 4×10^4 N
(d) 1×10^4 N
L1Difficulty 3
QTags Mechanical
QCereator Paper Maker 10

Q6. Heat is conducted through a 10 cm thick wall at the rate of 30 W/m² when the temperature difference across the wall is 10°C. What is the thermal conductivity of the wall?
(a) 0.03 W/mK
(b) 0.3 W/mK
(c) 3.0 W/mK
(d) 30.0 W/mK
L1Difficulty 3
QTags Mechanical
QCereator Paper Maker 10

Q7. The equation of effectiveness ε=1-e^(-NTU) of a heat exchanger is valid (NTU is number of transfer unit) in the case of
(a) boiler and condenser for parallel flow
(b) boiler and condenser for counter flow
(c) boiler and condenser for both parallel flow and counter flow
(d) gas turbine for both parallel flow and counter flow
L1Difficulty 3
QTags Mechanical
QCereator Paper Maker 10

Q8. In a governor, if the equilibrium speed is constant for all radii of rotation of balls, the governor is said to be
(a) stable
(b) unstable
(c) inertial
(d) isochronous
L1Difficulty 3
QTags Mechanical
QCereator Paper Maker 10

Q9. Which one of the following expresses the total elongation of a bar of length L
with a constant cross-section of A and modulus of elasticity E hanging vertically and subject to its own weight W?
(a) WL/AE
(b) WL/2AE
(c) 2WL/AE
(d) WL/4AE
L1Difficulty 3
QTags Mechanical
QCereator Paper Maker 10

Q10. Carbide tool is used to machine a 30 mm diameter steel shaft at a spindle speed of 1000 revolutions per minute. The cutting speed of the above turning operation is
(a) 1000 rpm
(b) 1570 m/min
(c) 94.2 m/min
(d) 47.1 m/min
L1Difficulty 3
QTags Mechanical
QCereator Paper Maker 10

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-T_2/T_1 =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.
It is an impossible engine.

S3. Ans (c)
Sol.

F_B/F_A =(ρg(2a)×a²)/(ρg(a)×2a²)=1

S4. Ans (b)
Sol. The draft tube has two purposes as follows:
It permits a negative or suction head to be established at the runner exist, thus making it possible to install the turbine above the tail race level without loss of head.
It converts a large proportion of velocity energy rejected from the runner into useful pressure energy. i.e. acts as a recuperetar of pressure energy.

S5. Ans (d)
Sol. (F_1 )/A_1 =F_2/A_2
⇒(16×10^4)/(π×(20)²)=F_2/(π(5)²)
∴F_2=1×10^4 N

S6. Ans (b)
Sol. Q=kA (ΔT )/l
⇒Q/A=kΔT/l
30=(k×10)/(10×10^(-2) )
⇒ k=30/100=0.3 W/mK

S7. Ans (c)
Sol. Heat capacity ratio C will be zero for both evaporator and condenser
C=0; ε=1-e^(-NTU)
This is valid for both evaporator and condenser

S8. Ans.(d)
Sol.

S9. Ans.(b)
Sol.

Deflection of elemental length ‘dx’.
d∆ =(W_x.d_x)/AE
Total deflection
∆ = ∫_0^2▒(W_x.d_x)/AE
W_x=V_x.γ=A.x.γ
Where γ = unit wt. of metal
∆= ∫_0^2▒(γ.A.x.dx)/AE
∆ =(γL^2)/2E=W/V×L^2/2E
∆=W/(A×L)×L^2/2E
∴∆=WL/2AE

S10. Ans.(c)
Sol.
Cutting speed,
V=πDN
=3.14×30×10^(-3)×1000
=3.14×30=94.2 m/min

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