Quiz: Mechanical Engineering 10th June

Quiz: Mechanical Engineering
Exam: AE/JE
Topic: Miscellaneous

Each question carries 1 mark
Negative marking: 1/3 mark
Time: 10 Minutes

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. Consider the following statements about true-stress-strain method:

1. It is more sensitive to changes in both metallurgical and mechanical conditions.
2. It gives a more accurate picture of the ductility.
3. It can be correlated with stress-strain values in other tests like torsion, impact,
   combined stress tests etc.
4. It can be used for compression tests as well.
   Which of the above statements are correct?
   (a) 1,2 and 3
   (b) 1,3 and 4
   (c) 2,3 and 4
   (d) All of the above

Q7. Detonation in the SI engine becomes severe during
(a) Low load and high speed
(b) High load and high speed
(c) Low load and low speed
(d) High load and low speed

Q8. The static friction
(a) bears a constant ratio to the normal reaction between the two surfaces
(b) is independent of the area of contact, between the two surfaces
(c) always acts in a direction, opposite to that in which the body tends to move
(d) all of the above

Q9. What happens to the specific volume of water when it is heated at 0°C?
(a) Decreases steadily
(b) Increases steadily
(c) first increases then decreases
(d) First decreases then increases

Q10. The Porter governor is an example of…………
(a) Inertia governor
(b) Flywheel governor
(c) Centrifugal governor
(d) None of these

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 (d)
Sol. True stress-strain curve is more sensitive to changes in both metallurgical and mechanical conditions, it can give a more accurate picture of the ductility and can be correlated with stress-strain values in other tests like torsion, impact, combined stress tests etc.

S7. Ans (d)
Sol. Detonation in SI engine will become severe at high load and low speed because at higher loads, the temperature of cylinder and combustion chamber walls will be higher and hence temperature of the end charge will be more which increases knocking tendency in SI engine and at lower engine speed, longer will be the absolute time for the flame to traverse the cylinder which increases the time available for pre flame reactions hence the tendency to knock increases.

S8. Ans.(d)
Sol. In case of static friction it is the ratio of Normal reaction between the surface to the friction force.
It is always opposing the motion or tending to motion of the body so always act in opposite direction.

S9. Ans.(d)
Sol. As, density of water is maximum at 4°C so when temperature of water is increased then upto 4°C specific volume decreases due to density increase and after that specific volume increase.

S10. Ans.(c)
Sol. Types of centrifugal governor.
(1) Watt governor
(2) Porter governor
(3) Proell governor
(4) Hartnell governor
In centrifugal governor, centrifugal force on balls will decide the sleeve movement and control the mean speed

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