Question

Two discs A and B of same material and thickness have radii R and 3R respectively. Their moments of inertia about their axis will be in the ratio ______.

Options

• 3:1

• 1:9

• 1:81

• 1:27

Answer 1

Two discs A and B of same material and thickness have radii R and 3R respectively. Their moments of inertia about their axis will be in the ratio 1:9.

Explanation:

The ratio of moments of inertia of two discs of the same mass and same thickness is given by, \[\frac{\mathrm{I}_1}{\mathrm{I}_2}=\frac{\mathrm{R}_1^2}{\mathrm{R}_2^2}\]

\[\therefore\] \[\frac {I_1}{I_2}\] = \[\frac {R^2}{(3R)^2}\] = \[\frac {1}{9}\]