# Mechanical Vibration MCQ

1. When there is a reduction in the amplitude of vibrations over every cycle of vibration, then the body is said to have

1. free vibrations
2. forced vibrations
3. damped vibrations
4. torsional vibrations

2. At a certain speed, revolving shafts tend to vibrate violently in transverse directions, this speed is known as

1. critical speed
2. whirling speed
3. whipping speed
4. All the above

3. Damping capacity of a material is its ability to

1. Absorb shocks
2. Absorb impact
3. Withstand creep failures
4. Absorb Vibrations

4. The torsional vibrational frequency of a shaft with n oscillating masses will be

1. n-1
2. n
3. 2n
4. n+1

5. In free vibrations, the acceleration vector leads the displacement vector by

1. π/3
2. π/2
3. 2π/3
4. π

6. At critical speed

1. the shaft runs smoothly
2. the shaft runs with noise due to vibration
3. the shaft becomes dynamically unstable with negligible lateral amplitudes
4. the shaft becomes dynamically unstable with

7. In a damped vibration system, the damping force is proportional to

1. Vibrations
2. Displacement
3. Velocity
4. Compression

8. In underdamped system the amplitude of vibration with reference to time

1. increases linearly
2. increases exponentially
3. decreases linearly
4. decreases exponentially

9. For steady state forced vibrations, the phase lag at resonance condition is

1. 45°
2. 90°
3. 80°

10. In the spring mass system, if the mass of the system is double with spring stiffness halved, the natural frequency of vibration is

1. remains unchanged
2. doubled
3. halved

11. If the period of oscillation is doubled

1. the length of simple pendulum should be doubled
2. the length of simple pendulum should be quadrupled
3. the mass of the pendulum should be doubled
4. the length and mass should be doubled

12. Seismic vibrations are measured with

1. Richter scale
2. Vibrometers
3. Accelerometers
4. Gyroscope

13. If the damping factor for a vibrating system is unity, then the system is

1. critically damped
2. underdamped
3. zero damped
4. overdamped

14. The amplitude ratio of two successive oscillations of a damped vibratory system is

1. more than one
2. less than one
3. variable
4. equal to one

15. Whirling speed of a shaft coincides with the natural frequency of the

1. longitudinal vibration
2. transverse vibration
3. All of above
4. None of the above

16. A shaft carrying two rotors as its ends will have

1. no node
2. one node
3. two node
4. three node

17. Critical speed of a shaft depends on

1. Diameter of disc
2. Length of shaft
3. Eccentricity
4. All of the above

18. A vibrating system with unity as damping factor will be

1. critically damped
2. damped to safe limits
3. partly damped
4. free from vibrations

19. Which of the following behaviour of the system defines under-damped harmonic oscillator?

1. The system returns (exponentially decays) to equilibrium without oscillating.
2. The system returns to equilibrium as quickly as possible without oscillating.
3. The system oscillates (at reduced frequency compared to the undamped case) with the amplitude gradually decreasing to zero.
4. The system oscillates at its natural resonant frequency.