A horizontal disc rotates freely with angular velocity `omega` about a vertical axes through its centre. A rig having the same mass and radius as the disc, is now gently placed coaxially on the disc. After some time, the two rotate with a common angular velocity. then.

Options

A. no friction exists between te disc and the ring
B. the angular momentum of the system is conserved
C. the final common angular velocity is `(1)/(2)omega`
D. all of the above

Explanation

`I_(1)omega_(1)=I_(2)omega_(2)`
`thereforeomega_(2)=((I_(1))/(I_(2)))omega_(1)=(((1)/(2)mR^(2)))/(((1)/(2)mR^(2)+mR^(2)))omega=(omega)/(3)`