Question

A circular disc is rotating with angular velocity $\omega$. If a man standing at the edge of the disc walks towards its centre then the angular velocity of the disc will.

• A. decrease
• B. increase
• C. be halved
• D. not changes

Answer 1

The correct option is B increase

When no external force acts on a body its angular moment remains conserved.
From law of conservation of angular momentum, we have
$J=l\omega =$constant
where l is moment of inertia of the body and $\omega$ is angular velocity.
Also $l=\frac{1}{2}M{R}^2$(for disc) where M is mass and R is radius of disc.
$J=\frac{1}{2}M{R}^2\omega =$ constant
Since, man moves towards the centre of the disc, distance of mass distribution R decreases hence, $\omega$ increases.