+1 vote
in Machine Dynamics by (34.3k points)
If the length of the disc is negligible, then what will be the moment of inertia about the diametral axis?

(a) mr^2/4

(b) mr^2

(c) mr^2/2

(d) 2mr^2

This question was posed to me at a job interview.

Origin of the question is Effect of Gyroscopic Couple on a Disc Fixed Rigidly at a Certain Angle to a Rotating Shaft in portion Gyroscopic Couple and Precessional Motion of Machine Dynamics

1 Answer

0 votes
by (38.6k points)
Right choice is (a) mr^2/4

Easiest 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 (l^2/12 + r^2/4), if l is negligible then the expression becomes

mr^2/4.

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