Quiz: Mechanical Engineering 23 June 2020 |_00.1
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Quiz: Mechanical Engineering 23 June 2020

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

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

Q1. Consider the following statements: An increase in pin fin effectiveness is caused by high value of
1. Convective coefficient
2. Thermal conductivity
3. Sectional area
4. Circumference
Which of the above statements are correct?
(a) 1 and 3
(b) 1 and 4
(c) 2 and 3
(d) 2 and 4

Q2. Ericsson Cycle consists of
(a) Two isochoric process and two isobars
(b) Two isothermal process and two isobars
(c) Two isochoric process and two isothermal process
(d) Two isochoric process and two isentropic process

Q3. When a liquid flow through a tube with sub-cooled or saturated boiling, what is the process known?
(a) Pool boiling
(b) Bulk boiling
(c) Convection boiling
(d) Forced convection boiling

Q4. Consider the following energies associated with a Pelton turbine:
1. Mechanical energy
2. Kinetic energy
3. Potential energy
The correct sequence of energy conversion starting from the entry of fluid is
(a) 1, 2 and 3
(b) 2, 3 and 1
(c) 3, 2 and 1
(d) 1, 3 and 2

Q5. There is no work transfer involved in this process
(a) Adiabatic expansion
(b) Isothermal expansion
(c) Polytropic expansion
(d) Free expansion

Q6. In order to double the period of simple pendulum
(a) the mass of its bob should be doubled
(b) the mass of its bob should be quadrupled
(c) its length should be doubled
(d) its length should be quadrupled

Q7. Duralumin is an alloy of
(a) Vanadium
(b) Aluminium
(c) Tungsten
(d) Iron

Q8. Window AC has an expansion device named as
(a) Expansion valve
(b) Thermostatic valve
(c) Capillary tube
(d) Piston-cylinder

Q9. An object weighs 40 N in air and 30 N, when submerged in water then specific gravity of body is
(a) 4/3
(b) 3/4
(c) 4
(d) 3

Q10. A thick lubrication is
(a) a stable lubrication and there is no metal to metal contact
(b) a stable lubrication because there is some amount of metal to metal contact
(c) an unstable lubrication because there is some amount of metal to metal contact
(d) an unstable lubrication because there is no metal to metal contact

Solutions

S1. Ans (d)
Sol.
∈(fin)=√(kP/hA)
∈ ∝ K^(1/2)
∈ ∝ P^(1/2)
Thus, fin effectiveness will increase if thermal conductivity and circumference increases.

S2. Ans (b)
Sol. Ericsson Cycle consists of two constant pressure processes and two isentropic processes.

S3. Ans (b)
Sol. Pool Boiling: In this case the liquid above the hot surface is essentially stagnant and its motion near the surface is due to free convection.
Forced Convection Boiling: This refers to a situation where the fluid motion is induced by external means. This type of boiling occurs in water tube boilers involving forced convection.
Sub-Cooled or Local Boiling: In this case the liquid temperature is below the saturation temperature and bubbles are formed in the vicinity of heat surface.
Saturated Boiling: Here, the liquid temperature exceeds the saturation temperature.

S4. Ans (c)
Sol. As water flows down the height its potential energy gets converted into kinetic energy, when water hits the runner, the kinetic energy gets converted into rotational mechanical energy of runner.

S5. Ans (d)
Sol. Since free expansion occurs against vacuum hence no work is done by the expanding fluid.

S6. Ans.(d)
Sol. We know that
T∝√L
T = Time period
L = Length of pendulum
In order to double the period of simple pendulum, its length should be quadrupled.

S7. Ans.(b)
Sol. Duralumin is an alloy, a trade name given to the earliest types of the age harden able aluminium alloys. It is an alloy made up of 90% aluminum,4% copper, 1% magnesium and 0.5% to 1% manganese.

S8. (c)
Sol. In window AC capillary tube is used as an expansion device as it is cost effective and simple.

S9. Ans.(c)
Sol. We know,
Buoyancy on body=weight of body in air-weight of body in water
=40-30
=10 N
specific gravity of solid body
=(density of body)/(density of standard liquid or water)
=(weight of body)/(buoyancy on body)
=40/10
=4

S10. Ans.(a)
Sol. A thick lubrication is a stable lubrication and there is no metal to metal contact.

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