Q1. A uniform disc of radius r is spinned about its axis to an angular velocity ω and then carefully placed with its plane on a rough horizontal surface. Find the time taken for the disc to stop rotating, given the coefficient of friction between the disc and the horizontal surface is μ. Assume that the disc exerts pressure on the horizontal surfcace uniformly.
106abhisek has got correct answer for Q1.
@abhisek: these questions are meant for remaining forever. (atleast a month)
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dτ=M μ g 2πx2dx
Ï€R2
integrate it frm 0 to R
τ=2/3μMgR
α=(2/3μMgR)Ic
Ic=MR2/2
α=4/3μg/R which is constant...
so time taken for ω to become 0 from ω0= ω0/α
hence the answer... 3ω0R/4μg
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106maybe but wat abt the other bits in Q2. Lemme check COR. wait.... COR wax not even asked. but i think ur right.