Quiz: Mechanical Engineering 10th July 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 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

Q2. Consider the following statements:
1. Free expansion of a gas
2. Slow heating of oil from a constant temperature source
3. Evaporation of water at its saturation temperature by a source at the same temperature
4. Isentropic compression of an ideal gas
Which of these processes are irreversible?
(a) 1 and 2
(b) 2 and 3
(c) 3 and 4
(d) 1 and 4

Q3. The predominant forces acting on an element of fluid in the boundary layer over a flat plate placed in a uniform stream include.
(a) inertia and pressure forces
(b) viscous and pressure forces
(c) viscous and body forces
(d) viscous and inertia forces

Q4. Heat transfer takes place according to
(a) Zeroth law of thermodynamics
(b) first law of the thermodynamics
(c) second law of thermodynamics
(d) third law of thermodynamics

Q5. Bernoulli’s equation is applicable between any two points located in
(a) Rotational flow of an incompressible fluid
(b) Irrotational flow of compressible or incompressible flow
(c) Steady, rotational flow of an incompressible fluid
(d) Steady, irrotational flow of an incompressible fluid

Q6. Properties of substances like pressure, temperature and density in thermodynamic coordinates are
(a) path functions
(b) point functions
(c) cyclic functions
(d) real functions

Q7. While designing a cam, pressure angle is one of the most important parameters which is directly proportional to
(a) pitch circle diameter
(b) prime circle diameter
(c) lift of cam
(d) base circle diameter

Q8. The speed rating for turbine rotors is invariably more than √2 times its natural frequency to
(a) increase stability under heavy load and high speed
(b) isolate vibration of the system from the surrounding
(c) minimize deflection under dynamic loading as well as to reduce transmissibility of force to the surrounding
(d) None of the above

Q9. In circular arc cam with a flat faced reciprocating follower, the contact between the follower and the nose of cam is only maintained if:
(a) External spring force is less than the inertia force of the follower
(b) External spring force is greater than the inertia force of the follower
(c) External spring force is zero
(d) The inertia force is more than the spring force

Q10. Seam welding is
(a) multi-spot-welding process
(b) continuous spot-welding process
(c) used to form mesh
(d) used for welding cylindrical objects

SOLUTIONS

S1. 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.

S2. Ans (d)
Sol.
(i) In isentropic compression process: Increase in entropy due to irreversibility is compensated by decrease in entropy due to heat loss and process becomes isentropic but not reversible.
(ii) Free expansion is always irreversible process due to absence of resistance against the expansion.
(iii) Slow heating is a quasi-static process which is reversible in nature.
(iv) Evaporation process is reversible.

S3. Ans.(d)
Sol. Reynolds number is used to characterize flow regimes, such as laminar flow and turbulent flow. It gives measure of the ratio of inertial force to viscous force. It consequently quantities the importance of boundary layer concept

S4. Ans.(c)
Sol. Heat transfer takes place according to second law of thermodynamics
Second law of thermodynamics states that “Heat will flow naturally from one reservoir to another at a lower temperature, but not in opposite direction without assistance”.

S5. Ans (d)
Sol. Bernoulli’s equation is applicable between any two points located in Steady, irrotational flow of an incompressible fluid.

S6. Ans.(b)
Sol. Properties of substances like pressure, temperature and density in thermodynamic coordinates are point functions.

S7. Ans.(d)
Sol. While designing a cam, pressure angle is one of the most important parameters which is directly proportional to base circle diameter.

S8. Ans.(b)
Sol. The speed rating for turbine rotors is invariably more than √2 times its natural frequency to isolate vibration of the system from the surrounding.

S9. Ans.(b)
Sol. When the cam contact force goes to zero, the cam and follower will separate. Large enough spring force is necessary to keep cam and follower in contact throughout the entire rotation. External spring force should be greater than inertia force of the follower to maintain positive contact. If external spring force is too large, there is possibility of higher contact stress leading to surface failure.

S10. Ans (b)
Sol. In seam welding overlapping sheets are gripped between two wheels or roller disc electrodes and current is passed to obtain either the continuous seam i.e. overlapping weld nuggets or intermittent seam i.e. weld nuggets are equally spaced. Welding current may be continuous or in pulses.

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