Question

The moment of inertia of a uniform circular disc about its diameter is 100 gcm^2. What is its moment of inertia about an axis perpendicular to its plane.

(a) 500 gcm^2

(b) 100 gcm^2

(c) 200 gcm^2

(d) 700 gcm^2

The question was posed to me in exam.

This interesting question is from Centripetal Force in section Kinematics of Engineering Physics I

Answer 1

Correct choice is (c) 200 gcm^2

To explain I would say: By theorem of perpendicular axes, moment of inertia of the disc about an axis perpendicular to its plane,

I = Sum of the moments of inertia about two perpendicular diameters

I = Id+Id=2×1/4×MR^2=2×1000= 200 gcm^2.