# Machine Dynamics Questions and Answers – Vibration Isolation and Transmissibility

This set of Machine Dynamics Multiple Choice Questions & Answers (MCQs) focuses on “Vibration Isolation and Transmissibility”.

1. Which of the following systems produce a vibration in the foundation?
a) Unbalanced machine
b) Balanced machine
c) Coupled machine
d) Uncoupled machine

Explanation: It has been observed that when an unbalanced machine is installed on the foundation, it produces vibration in the foundation which needs to be countered to create smooth working of the machine.

2. When a periodic disturbing force is applied to a machine, the force is transmitted to the foundation by the means of spring.
a) True
b) False

Explanation: Springs or dampers are mounted on the machine in order to reduce the vibrations produce but however they also transmit the disturbing periodic force to the machine.

3. Which of the following is correct regarding isolation factor?
a) Dimensionless quantity
b) Has Newton as its unit
c) Has joule as its Unit
d) Has Hz as its unit

Explanation: Isolation factor is a ratio of transmitted force to the applied force, since it is a ratio of two quantities having same dimension, it is a dimensionless quantity.

4. Which of the following is a type of transmitted force to the foundation?
a) Damping force
b) Undamping force
c) Tensile force
d) Torsional force

Explanation: The transmitted force consists of the following two forces which are perpendicular to each other namely: Spring or elastic force and damping force. This happens as both spring and damper is used in order to minimize vibrations.

5. If the damper is not provided and the system is in resonance, which of the following is the correct isolation factor?
a) 0
b) 1/2
c) 1/4
d) Infinity

Explanation: When the damper is not involved, the damping coefficient c becomes zero and isolation factor is given by:
1/(1-(ω/ωn))
Since during resonance, ω=ωn
isolation factor becomes infinite.

6. If isolation factor is negative, then what is the phase difference between transmitted and disturbing force?
a) 180°
b) 90°
c) 450°
d) 360°

Explanation: If the isolation factor is negative then the ratio ω/ωn is greater than 1, in this case the phase difference between the disturbing force and the transmitted force is 180°.

7. Which of the following is true regarding Ɛ>1?
a) Transmitted force is greater than applied force
b) Transmitted force is less than applied force
c) Spring force is less than applied force
d) Damping force is less than applied force

Explanation: if the isolation factor is greater than 1, then the ratio ω/ωn < √2, this means that there is a phase difference between the transmitted force and the disturbing force, where the transmitted force is greater than the applied force.

8. Isolation factor is twice the transmissibility ratio.
a) True
b) False

Explanation: The given statement is false as the isolation factor and the transmissibility ratio have the same value which is given by ratio of Transmitted force to the Applied force.

Sanfoundry Global Education & Learning Series – Machine Dynamics.