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, they rotate with a common angular speed.
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a
some friction exists between the disc and the ring.
b
the angular momentum of the disc plus ring is conserved.
c
the final common angular speed is 23rd of the initial angular velocity of the disc.
d
23rd of the initial kinetic energy changes to heat.
answer is A.
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Detailed Solution
By conservation of angular momentum,I1ωi=I1+I2ωfωf=ω1/3Ei=12I1ωi2Ef=12I1+I2ωf2 Ratio of the heat produced to initial kinetic energy =Ei−EfEi=23