Question

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, then -

• A. its angular velocity will decrease
• B. its angular velocity will increase
• C. its moment of inertia will increase
• D. its moment of inertia will decrease

Answer 1

Answer: (A), (C)

its moment of inertia will increase

When the disc with a central hole is heated, diameter of the hole as well as the outer diameter of disc increases. As a result of this, mass of the disc will now distributed farther away from its axis of rotation which means that moment of inertia $\left(I\right)$ will increase.
Now, according to the law of conservation of angular momentum,$I\omega =$ constant when there is no external torque. Hence, angular velocity $\left(\omega \right)$ will decrease to maintain the relation.
i.e Options (a) and (c) are correct.