Engineering Questions with Answers - Multiple Choice Questions

Home » MCQs » Aeronautical Engineering » Machine Dynamics MCQ – Balancing of a Single Rotating Mass By a Single Mass Rotating in the Same Plane

# Machine Dynamics MCQ – Balancing of a Single Rotating Mass By a Single Mass Rotating in the Same Plane

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

**
View Answer**

Answer: a

Explanation: Centrifugal force is given by the equation

Fc = mω^{2}r

using the given data

Fc = 50000 N.

Centrifugal force acts radially inwards and bends the shaft.

a) True

b) False

**
View Answer**

Answer: b

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.

The mass used to balance the mass defect is known as ______

a) Balancing mass

b) Defect mass

c) Replacement mass

d) Fixing mass

**
View Answer**

Answer: a

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.

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

**
View Answer**

Answer: b

Explanation: Centrifugal force is given by the equation

Fc = mω^{2}r

using the given data

Fc = 25000 N.

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

**
View Answer**

Answer: c

Explanation: Centripetal force is given by the equation

Fc = – mω^{2}r

This is the negative of the centrifugal force.

using the given data

Fc = -100000 N.

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

**
View Answer**

Answer: a

Explanation: Centrifugal force is given by the equation

Fc = mω^{2}r

using the given data

Fc = 25000 N

r = 0.2 m

ω = 50 rad/s

m = 50 kg.

From the given data, calculate the unbalanced centrifugal force in N s^{2}

Distance from shaft = 0.2 m

Mass = 100 kg

Rotating speed = 1000 rpm.

a) 20

b) 2×10^{7}

c) 200

d) 20000

**
View Answer**

Answer: a

Explanation: Centrifugal force is given by

Mω^{2}r

In N-s^{2} = m.r

= 100×0.2 = 20 N-s^{2}.

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

**
View Answer**

Answer: b

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