Quiz: Mechanical Engineering 9th July 2020

Quiz: Mechanical Engineering
Exam: UPPSC AE
Topic: Miscellaneous

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

Q1. In regarding nucleate boiling ___________
(a) The temperature of the surface is greater than the saturation temperature of the liquid
(b) Bubbles are created by expansion of entrapped gas or vapour at small cavities in the surface
(c) The temperature is greater than that of film boiling
(d) All options are correct

Q2. Calculate the power (in kW) required by the engine of a car travelling at the constant speed of 50 m/s. If the car has to resist a wind drag F_D=20V(in N), where V is the velocity of the car.
(a) 20
(b) 25
(c) 50
(d) 75

Q3. Water, by evaporating cooling, can be theoretically be cooled down to
(a) Atmospheric temperature
(b) Air dry bulb temperature
(c) Air wet bulb temperature
(d) Air dew point temperature

Q4. What is the location of frictional force when the intensity of pressure is uniform in a flat pivot bearing having radius r?
(a) r
(b) r/2
(c) 2r/3
(d) r/3

Q5. When the depth of water in an open channel is less than the critical depth, then flow is said to be
(a) critical
(b) turbulent
(c) torrential
(d) tranquil

Q6. In order that no shock wave develops when flow is taking place through a converging-diverging tube, Mach number at exit should be
(a) equal to 1
(b) greater than 1
(c) less than 1
(d) none of these

Q7. Which of the following is the correct method for the conversion of spring-controlled governor from unstable to stable?
(a) Increasing the ball weight
(b) Decreasing the spring stiffness
(c) Decreasing the ball weight
(d) Increasing the spring stiffness

Q8. Which one of the following assumptions in the theory of pure torsion is false?
(a) The angle of twist is uniform along the length
(b) The shaft is of uniform circular section throughout
(c) Cross-section plane before torsion remains plane after torsion
(d) All radii get twisted due to torsion

Q9. Filling or decking in a cooling tower increases the rate of heat transfer by providing
(a) increased flow of water
(b) increased flow of air
(c) increased flow of water and air
(d) a large amount of wetted surface

Q10. Two-stroke engines are used more frequently in two wheelers due to which of the following reasons?
(a) exhaust is less
(b) higher thermal efficiency
(c) higher power to weight ratio
(d) less friction

Solutions

S1. Ans.(a)
Sol. Nucleate boiling is a type of boiling that takes place when the surface temperature is hotter than the saturated fluid temperature by a certain amount but where the heat flux is below the critical heat flux.

S2. Ans.(c)
Sol. We know that
Power required = F_D×V
= 20×V×V
= 20×50^2
= 50 kW

S3. Ans.(c)
Sol. By evaporating cooling, air can be cooled down to its wet bulb temperature. Evaporative cooling is a process that uses the effect of evaporation as a natural heat sink. Sensible heat from the air is absorbed to be used as latent heat necessary to evaporate water.

S4. Ans.(c)
Sol. The frictional force acts at 2r/3 distance from the center when intensity of pressure is given uniform.

S5. Ans.(c)
Sol. When the depth of water in an open channel is less than the critical depth, then flow is said to be torrential.

S6. Ans.(b)
Sol. Mach number at exit should be greater than 1 for no shock wave generation when flow is taking place through a converging-diverging tube.

S7. Ans.(b)
Sol. A spring-controlled governor is said to be stable if the radius of the balls increases with increase in the speed of the governor and vice versa. A spring-controlled governor can be made stable by decreasing the spring stiffness.

S8. Ans.(a)
Sol. Following assumptions are made in the theory of pure torsion:
The material of shaft is uniform throughout
The shaft is of uniform circular cross-section throughout its length
Cross section remains plane before and after torsion.
All radii get twisted due to torsion

S9. Ans.(d)
Sol. Filling or decking in a cooling tower increases the rate of heat transfer by providing increased wetted area.

S10. Ans.(c)
Sol. Two-stroke engines are used more frequently in two wheelers due to higher power to weight ratio of these engines.

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