Question

A disc is spinning with an angular velocity? rad/s about the axis of spin. The couple applied to the disc causing precession will be

(a) 1/2Iω^2

(b) Iω^2

(c) 1/2 Iω ωp

(d) Iω ωp

This question was posed to me by my college professor while I was bunking the class.

This intriguing question comes from Precessional Angular Motion topic in chapter Gyroscopic Couple and Precessional Motion of Machine Dynamics

Answer 1

The correct choice is (d) Iω ωp

The best explanation: Since the rate of change of angular momentum will result by the application of a couple to the disc, therefore the couple applied to the disc causing precession,

Iω ωp

where I = Mass moment of inertia of the disc, and

ωp = Angular velocity of precession of the axis of spin.