Quiz: Mechanical Engineering 1 April 2020

Quiz: Mechanical Engineering 1 April 2020
Exam: USSSC JE
Topic: Miscellaneous

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

Q1. The centre of pressure for an inclined surface area
(a) Lies below the centroid of the surface
(b) Coincides with the centroid
(c) Lies above the centroid of the surface
(d) None of the above
L1Difficulty 3
QTags Mechanical
QCereator Paper Maker 10
Q2. A bucket of water hangs with a spring balance. If an iron piece is suspended into water from another support without touching the sides of the bucket, the spring balance will show
(a) an increased reading
(b) a decreased reading
(c) no change in reding
(d) increased or decreased reading depending on the depth of immersion
L1Difficulty 3
QTags Mechanical
QCereator Paper Maker 10
Q3. Match List-I (Measuring device) with List-II (Parameters) regarding a body partly submerged in a liquid and select the correct answer using the codes given below the lists:
List-I List-II
A. Anemometer 1. Flow rate
B. Piezometer 2. Velocity
C. Pitot tube 3. Static pressure
D. Orifice 4. Difference between static and stagnation pressure
Codes :
A B C D
(a) 1 3 4 2
(b) 1 2 3 4
(c) 2 3 4 1
(d) 2 4 3 1
L1Difficulty 3
QTags Mechanical
QCereator Paper Maker 10
Q4. Priming is necessary in
(a) Centrifugal pumps to lift water from a greater depth
(b) centrifugal pumps to remove air in the suction pipe and casing
(c) Hydraulic turbine to remove air in the turbine casing
(d) Hydraulic turbine to increase the speed of turbine and to generate more power
L1Difficulty 3
QTags Mechanical
QCereator Paper Maker 10
Q5. Match List-I with List-II and select the correct answer using the codes given below the lists:
List I
Work done in a polytropic process
Work done in steady flow process
Heat transfer in a reversible adiabatic process
Work done in an isentropic process
List- II
-∫▒Vdp
Zero
(p_1 V_1-p_2 V_2)/(γ-1)
4. (p_1 V_1-p_2 V_2)/(n-1)
Codes
A B C D
(a) 4 1 3 2
(b) 1 4 2 3
(c) 4 1 2 3
(d) 1 2 3 4
L1Difficulty 3
QTags Mechanical
QCereator Paper Maker 10
Q6. In a heat engine operating in a cycle between a source temperature of 606°C and a sink temperature of 20°C, what will be the least rate of heat rejection per kW net output of the engine?
(a) 0.50 kW
(b) 0.667 kW
(c) 1.5 kW
(d) 0.0341 kW
L1Difficulty 3
QTags Mechanical
QCereator Paper Maker 10
Q7. Match list I with list II and select the correct answer using the codes given below the lists:
List – I List – II
A. Bell Coleman refrigeration 1. Compressor
B. Vapour compression refrigeration 2. Generator
C. Absorption refrigeration 3. Flash chamber
D. Jet refrigeration 4. Expansion cylinder
codes
A B V D
(a) 1 4 3 2
(b) 4 1 3 2
(c) 1 4 2 3
(d) 4 1 2 3
L1Difficulty 3
QTags Mechanical
QCereator Paper Maker 10
Q8. The knocking tendency in compression ignition engines increases with
(a) increase of coolant water temperature
(b) increase of temperature of inlet air
(c) decrease of compression ratio
(d) increase of compression ratio
L1Difficulty 3
QTags Mechanical
QCereator Paper Maker 10
Q9. Dimensionless time is represented by
(a) Biot number
(b) Fourier number
(c) Euler number
(d) Graetz number
L1Difficulty 3
QTags Mechanical
QCereator Paper Maker 10
Q10. In a counter flow heat exchanger, the product of specific heat and mass flow rate is same for the hot and cold fluids. If NTU is equal to 0.5 then the effectiveness of the heat exchanger is
(a) 1.0
(b) 0.5
(c) 0.33
(d) 0.2
L1Difficulty 3
QTags Mechanical
QCereator Paper Maker 10

SOLUTIONS
S1. Ans.(a)
Sol.
h=x ̅+I_G/(Ax ̅ ) sin^2 θ
x ̅ = Centre of gravity
I_G = Area moment of inertia of surface about its centroidal axis and parallel to free surface.
S2. Ans.(c)
Sol.
Since the water of bucket will exert force of buoyancy equal to the volume displaced by the iron block. Hence equal and opposite force will be exerted by iron block on water hence the reading of the spring balance will increase.
S3. Ans.(c)
Sol.
Anemometer: It is device for measuring wind speed, and it a common weather station instrument.
Orifice plate: It is a device used for measuring the volumetric flow. It uses the Bernoulli’s principle.
S4. Ans.(b)
Sol. filling the pump casing and the suction pipe with the liquid before it is started is known as priming. Unless the centrifugal pump is primed, it will not start as there is no centrifugal head impressed on the liquid. Positive displacement type reciprocating or rotary pump do not need priming because the air, if any, in the cylinder or casing is driven out by the piston or vanes.
S5. Ans.(c)
Sol.
A. Work done in a polytropic process: (p_1 V_1-p_2 V_2)/(n-1)
B. Work done in steady flow process -∫▒Vdp
C. Heat transfer in a reversible adiabatic process: zero
D. Work done is an isentropic process: (p_1 V_1-p_2 V_2)/(γ-1)
S6. Ans.(a)
Sol.

T_1=606+273=879 K
T_2=20+273=293 K
η=(T_1-T_2)/T_1
=(879-293)/879=W/Q_1 (since W = 1 kW)
0.6666=〖1/Q〗_1
Q_1=1.5 kW
Amount of heat rejected
Q_2=Q_1-W=1.5-1.0=0.5 kW
S7. Ans.(d)
Sol.
1. Bell Coleman refrigeration: Expansion cylinder
2. Vapour compression refrigeration: compressor
3. Absorption refrigeration: Generator
4. Jet Refrigeration: Flash chamber
S8. Ans.(c)
Sol.
Decrease of compression ratio will reduce temperature and increase delay period. This increases the knocking tendency in CI engine.
S9. Ans.(b)
Sol. Dimensionless time is represented by Fourier number.
Mathematically, Fourier number = (αt )/(L_C^2 )
Where
α = Thermal diffusivity
=(k/ρC)
L_C = characteristics length
t = time
S10. Ans.(c)
Sol. C=1
∴ ε=NTU/(1+NTU)
ε=0.5/1.5=1/3=0.33

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