Question

A thin uniform circular disc of Mass M and radius R is rotating in a Horizontal plan about an axis passing through it's center and perpendicular to it's plane with an angular velocity.
Another Disc of the same dimensions but of Mass M/4 is placed gently on the first disc co-axially.
Show that angular velocity of the system is 4/5w.

Answer 1

heya !!



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Answer 2

Hence proved





Please see the pic for answer





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