Engineering Questions with Answers - Multiple Choice Questions

# Machine Dynamics MCQ – Free Torsional Vibrations of a Single Rotor System

1 - Question

Which of the following relation is correct regarding free torsional vibrations of a single motor system?
a) Independent of modulus of rigidity
b) Independent of polar moment of inertia
c) Dependent on mass moment of inertia
d) Independent of length of shaft

Explanation: The free torsional vibrations of a single motor system depends on the following factors:
Modulus of rigidity, Polar moment of inertia, mass moment of inertia and length of the shaft.

2 - Question

Free torsional vibrations of a single motor system increases with increase in polar moment of inertia.
a) True
b) False

Explanation: The free torsional vibrations of a single motor system depends on the following factors:
√Polar moment of inertia as directly proportional to the square root of polar moment of inertia.

3 - Question

If the polar moment of inertia is increased to four times, then what will be the effect on free torsional vibrations of a single motor system?
a) Increases 4 times
b) Increases 2 times
c) Decreases 4 times
d) Decreases 2 times

Explanation: Since the free torsional vibrations of a single motor system depend on the square root of the polar moment of inertia of the system, increasing 4 times will lead to increase in two times the initial vibration.

4 - Question

If the mass moment of inertia is increased to four times, then what will be the effect on free torsional vibrations of a single motor system?
a) Increases 4 times
b) Increases 2 times
c) Decreases 4 times
d) Decreases 2 times

Explanation: Since the free torsional vibrations of a single motor system depend on the inverse of square root of the mass moment of inertia of the system, increasing 4 times will lead to decrease in two times the initial vibration.

5 - Question

Calculate the free torsional vibrations of a single motor system from the following data:
C = 8 GN/m2, L=9m, I = 600 Kg-m2, J = 8×104 m4
a) 162,132
b) 172,132
c) 182,132
d) 192,132

Explanation: The free torsional vibrations of a single motor system is given by
12(C.J÷l.I)−−−−−−−−−√
Substituting the given values gives f = 172132 Hz.

6 - Question

If the length inertia is decreased to nine times, then what will be the effect on free torsional vibrations of a single motor system?
a) Increases 3 times
b) Increases 9 times
c) Decreases 9 times
d) Decreases 3 times

Explanation: Since the free torsional vibrations of a single motor system depends on the inverse of square root of the length, decreasing 9 times will lead to increase in 3 times the initial vibration.

7 - Question

Calculate the Polar moment of inertia in m4 of a single motor system from the following data:
C = 8 GN/m2, L=9m, I = 600 Kg-m2, f=10 Hz
a) 0.00027
b) 0.00032
c) 0.00045
d) 0.00078

Explanation: The free torsional vibrations of a single motor system is given by
12(C.J÷l.I)−−−−−−−−−√
Substituting the given values gives J = 0.00027 m4.

8 - Question

If radius of gyration increases then the torsional free vibration increases.
a) True
b) False