Question

Q. 11



a horizontal disc rotates freely with angular velocity '' about a vertical axis through its centre. A ring, having the same mass and as the disc, is gently placed on the disc. The common angular velocity with which the two rotate, will be

Answer 1

As ring is gently placed

So torque will be 0

therefore angular momentum is conserved

let w be common angular velocity

initial angular momentum = 1/2 m r^2 W = ( 1/2 mr^2 + mr^2) w

= 1/2W = 3/2 w

w = W/3