# Quiz:Mechanical Engineering 21 July 2020

Quiz: Mechanical Engineering
Exam: ISRO (TECHNICAL ASST.)
Topic: Miscellaneous

Each question carries 4 mark.
Negative marking: 1 mark
Time: 15 Minute

Q1. The entropy-increase of the solid substance as it melts into liquid at 27℃ (latent heat of fusion of substance = 300 kJ/kg)
(a) 14.8 kJ/kg-K
(b) 120 kJ/kg-K
(c) 10.8 kJ/kg-K
(d) 1 kJ/kg-K

Q2. The statement that molecular weight of all gases occupies the same volume is known as
(a) Avogadro’s hypothesis
(b) Gas law
(c) Dalton’s law
(d) Thermodynamics law

Q3. Critical speed of a turbine is
(a) same as run-away speed
(b) speed that will cause mechanical failure of the shaft
(c) speed at which natural frequency of vibrations equals the number of revolutions of the same time
(d) speed equal to synchronous speed of the generator

Q4. A curve showing the variation of load on a power station with respect to time is known as
(a) Load curve
(b) Load duration curve
(c) Diversity factor
(d) Performance curve

Q5. Problem of scavenging appears in case of
(a) Petrol engine
(b) Diesel engine
(c) Four-stroke engine
(d) Two-stroke engine

Q6. Consider the following statements with respect to evaporative cooling process:
1. The wet-bulb temperature remains constant.
2. The dew point temperature remains constant.
3. The enthalpy remains constant.
Which of the statements are correct?
(a) 1, 2 and 3
(b) 1 and 3 only
(c) 2 and 3 only
(d) 1 and 3 only

Q7. Select the correct statement:
(a) Viscosity of a gas increases with temperature
(b) Density of a gas increases with temperature
(c) Surface tension of a liquid increases with temperature
(d) Bulk modulus of elasticity is independent of temperature

Q8. The safeguarding structure provided in the dam to relieve the reservoir of excess water when the water level in the reservoir rises, is known as:
(a) Spillways
(b) Draft tube
(c) Catchment area
(d) Surge tank

Q9. The potential energy an elevator loses in coming down from the top of a building to stop at the ground floor is
(a) lost to the driving motors
(b) converted into heat
(c) lost in friction of the moving surface
(d) used up in lifting the counter poise weight

Q10. Which of the following is not an example of plastic?
(a) polyethylene, polystyrene
(b) Poly ethylene tetraphthalate
(c) Poly vinyl chloride
(d) Kovar

Solutions

S1. Ans (d)
Sol. We know that
Entropy-increase (∆S)=LH/T=300/300
= 1 kJ/kg-K

S2. Ans (a)
Sol. Avogadro’s law states that under the same conditions of temperature and pressure, equal volumes of different gases contain an equal number of molecules.

S3. Ans (c)
Sol. Critical speed is that speed of turbine at which speed of revolutions equals to natural frequency of revolutions of the system.

S4. Ans (a)
Sol. Load curve is the variation of load with time on a Power Station. As the load on a Power Station never remain constant rather it varies time to time, these variations in load is plotted on half hourly or hourly basis for the whole day. The curve thus obtained is known as Daily Load Curve.

S5. Ans (d)
Sol. Since, one engine cycle in a two-stroke engine is completed in one crankshaft rotation, gas exchange has to occur while the piston is near BDC. This process of simultaneously purging exhaust gas from the previous cycle and filling the cylinder with fresh charge for a new cycle is referred to as scavenging.

S6. Ans (d)
Sol. During evaporative cooling process, enthalpy and wet bulb temperature remains constant but DBT decreases and specific humidity along with relative humidity increases.

S7. Ans (a)
Sol. Viscosity of gas increases with temperature due to increase in momentum and viscosity of liquid decreases with temperature due to increases in molecular space.

S8. Ans (a)
Sol. A spillway is a structure used to provide the controlled release of flows from a dam or levee into a downstream area, typically the riverbed of the dammed river itself.

S9. Ans (d)
Sol. The potential energy an elevator loses in coming down from the top of a building to stop at the ground floor is used up in lifting the counter poise weight.

S10. Ans (d)
Sol. Kovar is not a type of plastic, but it is actually an iron nickel-cobalt alloy.

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