# Machine Dynamics Questions and Answers – Effect of Gyroscopic Couple on a Disc Fixed Rigidly at a Certain Angle to a Rotating Shaft

This set of Machine Dynamics Interview Questions and Answers for freshers focuses on “Effect of Gyroscopic Couple on a Disc Fixed Rigidly at a Certain Angle to a Rotating Shaft”.

1. In the figure given below, the moment of inertia about polar axis OP is _______

a) mr2/2
b) mr2
c) 2mr2
d) 4mr2

Explanation: In the figure given above, if m is the mass of the disk and r is the radius, then the moment of inertia about the axis OP is given by mr2/2.

2. When seen from the top, the gyroscopic couple acting on the disc will act in the clockwise direction.
a) True
b) False

Explanation: When seen from the top, the gyroscopic couple acting on the disc will act in the anti-clockwise direction.

3. In the figure given below, the moment of inertia about diametral axis is _______

a) m(l2/12 + r2/4)
b) m(l2/6 + r2/4)
c) m(l2/12 + r2/2)
d) m(l2/12 + r2)

Explanation: If m is the mass, l is the length and r is the radius of the disc, then the moment of inertia about the diametral axis is given by m(l2/12 + r2/4).

4. If the length of the disc is negligible, then what will be the moment of inertia about the diametral axis?
a) mr2/4
b) mr2
c) mr2/2
d) 2mr2

Explanation: If m is the mass, l is the length and r is the radius of the disc, then the moment of inertia about the diametral axis is given by m (l2/12 + r2/4), if l is negligible then the expression becomes
mr2/4.

5. If the length and radius of the disc is same them moment of inertia is more about which axis?
a) Polar
b) Diametral
c) Shaft
d) Center

Explanation: If the length and radius are same then the moment of inertia will be more about the polar axis. Mr2/2 as compared to mr2/3.

6. From the following data calculate the gyroscopic couple on the bearing in N-m.
Mass of disc = 30 Kg, diameter = 60 cm
Rotation speed = 1200 rpm
Angle between disc and a plane 90 degree to the axis of shaft = 1°
a) 180
b) 186
c) 190
d) 196

Couple acting on the bearings
= mω2r2/8 sin2θ
substituting the values we get
C = 186 N-m.

7. If the rotation speed of the disc is increased to 2 times and the mass is reduced to half, overall the Couple acting on bearings will increase.
a) True
b) False

Explanation: If the rotation speed of the disc is increased to 2 times and the mass is reduced to half, overall the Couple acting on bearings will increase as couple on bearing depends on the relation
2r2/8 sin2θ, hence it will increase by two times.

Sanfoundry Global Education & Learning Series – Machine Dynamics.

To practice all areas of Machine Dynamics for Interviews, here is complete set of 1000+ Multiple Choice Questions and Answers.