# Machine Dynamics Questions and Answers – Balancing of a Single Rotating Mass By a Single Mass Rotating in the Same Plane

This set of Machine Dynamics online quiz focuses on “Balancing of a Single Rotating Mass By a Single Mass Rotating in the Same Plane”.

1. Let the disturbing mass be 100 kg and the radius of rotation be 20 cm and the rotation speed be 50 rad/s, then calculate the centrifugal force in kN.
a) 50
b) 25
c) 50000
d) 25000

Explanation: Centrifugal force is given by the equation
Fc = mω2r
using the given data
Fc = 50000 N.

2. Centrifugal force acts radially inwards and bends the shaft.
a) True
b) False

Explanation: We know that the centrifugal force exerted by the mass on the shaft, this centrifugal force acts radially outwards and thus produces bending moment on the shaft.

3. The mass used to balance the mass defect is known as ______
a) Balancing mass
b) Defect mass
c) Replacement mass
d) Fixing mass

Explanation: Disturbing mass causes centrifugal force and bending of the shaft, this mass is balanced by counteracting the shaft with another mass known as balancing mass.

4. Let the disturbing mass be 100 kg and the radius of rotation be 10 cm and the rotation speed be 50 rad/s, then calculate the centrifugal force in kN.
a) 50
b) 25
c) 50000
d) 25000

Explanation: Centrifugal force is given by the equation
Fc = mω2r
using the given data
Fc = 25000 N.

5. Let the disturbing mass be 200 kg and the radius of rotation be 20 cm and the rotation speed be 50 rad/s, then calculate the centripetal force in kN.
a) -50
b) -25
c) -100
d) -2500

Explanation: Centripetal force is given by the equation
Fc = – mω2r
This is the negative of the centrifugal force.
using the given data
Fc = -100000 N.

6. Let the centrifugal force in kN be 25 and the radius of rotation be 20 cm and the rotation speed be 50 rad/s, then calculate the mass defect in Kg.
a) 50
b) 25
c) 50000
d) 25000

Explanation: Centrifugal force is given by the equation
Fc = mω2r
using the given data
Fc = 25000 N
r = 0.2 m
m = 50 kg.

7. From the given data, calculate the unbalanced centrifugal force in N s2
Distance from shaft = 0.2 m
Mass = 100 kg
Rotating speed = 1000 rpm.
a) 20
b) 2×107
c) 200
d) 20000

Explanation: Centrifugal force is given by
2r
In N-s2 = m.r
= 100×0.2 = 20 N-s2.

8. In balancing of single-cylinder engine, the rotating unbalance is ____________
a) completely made zero and so also the reciprocating unbalance
b) completely made zero and the reciprocating unbalance is partially reduced
c) partially reduced and the reciprocating unbalance is completely made zero
d) partially reduced and so also the reciprocating unbalance

Explanation: In balancing of single-cylinder engine, the rotating unbalance is completely made zero and the reciprocating unbalance is partially reduced.

Sanfoundry Global Education & Learning Series – Machine Dynamics.