Question

A circular disc A and a ring B have same mass and same radius. If they are rotated with the same angular speed about their own axis, then

• A. A has less moment of inertia than B
• B. A has less rotational kinetic energy than B
• C. A and B have the same angular momentum
• D. A has greater angular momentum than B
• E. A has the same moment of inertia as that of B

Answer 1

Answer: (A)

Moment of inertia of disc
$I_{disc}=\frac{M{R}^2}{2}$
Moment of inertia of ring $I_{\text{ring }}=M{R}^2$ Therefore, A has less moment of inertia than B because of which A has less rotational kinetic energy than $B$.