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A horizontal disc rotating freely about a vertical axis makes 90 revolutions per minute. A small piece of wax of mass “m” falls vertically on the disk & sticks to it at a distance “r” from the axis. If the number of revolutions reduces to 60, then find the moment of inertia of the disc?
1. mr2
(the last ‘2’in each option should be considered as square, please)

  • physics -

    Conservation of momentum is applied.
    Momentum before=momentum after
    I disk*(90*2PI/60)=Idisk(60*2PI/60)+mr^2*60(2PI/60)
    solve for I disk.

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