A metallic circular disc having a circular hole at its centre rotates about an axis passing through its centre and perpendicular to its plane. When the disc is heated:

Options

A. angular speed increases but moment of inertia decreases
B. angular speed decreases but moment of inertia increases
C. angular speed and moment of inertia both decrease
D. angular speed and moment of inertia both increase.

Answer

B

Explanation

As the temperature of the circular disc increases, then due to thermal expansion, the diameter of the disc as well that of the circular hole will increase. Therefore, the moment of inertia . will increase resulting in a decrease in angular speed (from law of conservation of angular momentum).