Engineering Questions with Answers - Multiple Choice Questions
Machine Dynamics MCQ – Balancing of Rotating Masses
1 - Question
Often an unbalance of forces is produced in rotary or reciprocating machinery due to the ______
a) Centripetal forces
b) Centrifugal forces
c) Friction forces
d) Inertia forces
View Answer
Answer: d
Explanation: Often an unbalance of forces is produced in rotary or reciprocating machinery due to the inertia forces associated with the moving masses.
2 - Question
Balancing of single rotating mass by balancing masses in same plane and in different planes cannot take place.
a) True
b) False
View Answer
Answer: b
Explanation: Balancing of single rotating mass by balancing masses in same plane and in different planes can be done with the help of both static balancing and dynamic balancing.
3 - Question
Which of the following is true for centrifugal force causing unbalance?
a) Direction changes with rotation
b) Magnitude changes with rotation
c) Direction and magnitude both change with rotation
d) Direction and magnitude both remain unchanged with rotation
View Answer
Answer: a
Explanation: Force acting radially outwards acts on the axis of rotation and is known as centrifugal force. This is a disturbing force on the axis of rotation, the magnitude of which is constant but the direction changes with the rotation of the mass.
4 - Question
In a revolving rotor, the centrifugal force remains balanced as long as the centre of the mass of the rotor lies ___________
a) Below the axis of shaft
b) On the axis of the shaft
c) Above the axis of shaft
d) Away from the axis of shaft
View Answer
Answer: b
Explanation: In a revolving rotor, the centrifugal force remains balanced as long as the centre of the mass of the rotor lies on the axis of shaft. In other cases, the system will be unbalanced.
5 - Question
If the unbalanced system is not set right then.
a) Static forces develop
b) Dynamic forces develop
c) Tangential forces develop
d) Radial forces develop
View Answer
Answer: a
Explanation: It is very essential that all the rotating and reciprocating parts should be completely balanced as far as possible, otherwise the dynamic forces will be set up.
6 - Question
What is not the effect of unbalanced forces?
a) Load on bearings
b) Dangerous vibrations
c) Stresses in various members
d) Violation of conservation of mass principle
View Answer
Answer: d
Explanation: The unbalanced forces increase the loads on bearings and stresses in the various members, as well as it produces unpleasant and even dangerous vibrations.
7 - Question
What is the effect of a rotating mass of a shaft on a system?
a) Bend the shaft
b) Twist the shaft
c) Extend the shaft
d) Compress the shaft
View Answer
Answer: a
Explanation: Whenever an object containing mass is attached to a rotating shaft, it exerts some centrifugal force. This centrifugal force’s effect is to bend the shaft and to produce vibrations in it.
8 - Question
Balancing of reciprocating masses is the process of providing the second mass in order to counteract the effect of the centrifugal force of the first mass.
a) True
b) False
View Answer
Answer: b
Explanation: The process of providing the second mass in order to counteract the effect of the centrifugal force of the first mass, is called balancing of rotating masses. The main objective of balancing is to minimize the unbalanced forces.