Quiz:Mechanical Engineering 28 May 2020

Quiz: Mechanical Engineering
Exam: UPPSC AE
Topic: Miscellaneous

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

Q1. When an impeller has backward curved vanes in a centrifugal blower, then with an increase in flow rate, Euler head H
(a) increases
(b) decreases
(c) remains constant
(d) none of the above

Q2. C.I. engine as compared to S.I. engine require
(a) No flywheel
(b) Same size flywheel
(c) Smaller flywheel
(d) Bigger flywheel

Q3. The leakage in a refrigeration system using ammonia is detected by
(a) Halide torch
(b) Sulphur sticks
(c) Soap solution
(d) Hot water

Q4. A steam pipe is to be insulated by two insulating materials put over each other. For best results
(a) Better insulation should be put over pipe and inferior one over it.
(b) Inferior insulation should be put over pipe and better one over it
(c) Both may be put in any order
(d) Whether to put inferior one over pipe or the better one would depend on steam temperature

Q5. Consider the following phenomenon
1.Boiling
2.Free convection in air
3.Forced convection
4.Conduction in air
There correct sequence in the increasing order of heat transfer is
(a) 4, 2, 3, 1
(b) 1, 2, 3,4
(c) 4, 3, 2, 1
(d) 3, 4, 2, 1

Q6. Newton’s law of viscosity is about
(a) Ideal fluid
(b) Velocity gradient and rate of shear strain relation
(c) Shear deformation and shear stress relation
(d) Pressure and volumetric strain

Q7. The parameters which determine the friction factor for turbulent flow in a rough pipe are:
(a) Froud number and relative roughness
(b) Froud number and Mach number
(c) Reynolds number and relative roughness
(d) Mach number and relative roughness

Q8. A body of mass 20 kg is lifted up through a height of 4 m. How much work is done? (take g = 9.81 m/s^2)
(a) 648 J
(b) 684 J
(c) 748 J
(d) 784 J

Q9. Stress concentration occurs when:
(a) a body is subjected to excessive stress
(b) a body is subjected to unidirectional stress
(c) a body is subjected to fluctuating stress
(d) a body is subjected to non-uniform stress distribution

Q10. For a single row angular contact ball bearing, the basic dynamic capacity is 55 kN and the dynamic equivalent load is 3950 N. The rated life of the bearing is:
(a) 2700 million revolutions
(b) 2200 million revolutions
(c) 1700 million revolutions
(d) 1200 million revolutions

Solutions

S1. Ans.(b)
Sol. When we increase flow rate in a backward curved vane centrifugal compressor then Euler head decreases.

S2. Ans.(d)
Sol. C.I. engine as compared to S.I. engine requires bigger flywheel because of large torque carrying capacity of C.I. engine.

S3. Ans.(b)
Sol. Leakage in refrigeration system is detected by using sulphur sticks. Pass the stick over and around the area where you suspect the ammonia leak. If the sulphur stick begins to emit white smoke, this indicates the presence of ammonia.

S4. Ans.(a)
Sol. Better insulation should be put on the pipe to avoid any heat transfer from pipe and inferior one has to be put on above the better insulation for efficient insulation of the pipe.

S5. Ans.(a)
Sol. Correct sequence of increasing order of heat transfer is
Conduction in air < Free convection < Forced convection < Boiling

S6. Ans.(c)
Sol. Newton’s law of viscosity shows the relation between Shear stress and rate of shear strain. i.e. τ=μ du/dy.
τ=shear stress
du/dy=Rate of shear strain

S7. Ans.(c)
Sol. Friction factor for Turbulent flow is a function of Reynolds number and relative roughness. But for laminar flow, it is only a function of Reynolds number.

S8. Ans.(d)
Sol. Work done to lift a mass of 20 kg up to 4 m
W = force × distance
W = m×g×h
W = 20×9.81×4
W = 784.8 N-m or 784.8 J

S9. Ans.(d)
Sol. Stress concentration occurs when there is sudden change in the geometry of the object. It may be due to cracks, sharp corners, holes etc. All of these creates non-uniform stress distribution.

S10. Ans.(a)
Sol. Given,
Basic dynamic capacity = 55 kN
Dynamic equivalent load = 3950 N
For ball bearing, n = 3
Life=((Dynamic capacity)/(Dynamic equivalent load))^n
=(55000/3950)^3
=2699.8 or 2700 million revolutions

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