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:

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

Answer 1

Answer: (A), (C)

its moment of inertia will increase

When the disc with a central hole is heated, diameter of hole as well as outer diameter of disc both increases.
As a result of this, mass of the disc will be distributed more away from its axis, which means that moment of inertia will increase on heating.
According to the law of conservation of angular momentum, as $I\omega =$ constant, So $\omega$ will decrease.