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A horizontal disc rotates freely about a...

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

A

Some friction exists between the disc and the ring

B

The angular momentum of the 'disc plus ring' is conserve

C

The final common angular velocity is `(2)/(3)rd` of the initial angular velocity of the disc

D

`(2)/(3)rd` of the initial kinetic energy changes to heat.

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The correct Answer is:
a, b, d
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