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+1 vote
13.6k views
in Physics by (50.3k points)

A flywheel rotates about an axis. Due to friction at the axis, it experiences an angular retardation proportional to its angular velocity. If its angular velocity falls to half while it makes n rotations, how many more rotations will it make before coming to rest? 

(a) 2n 

(b) n 

(c) n/ 2 

(d) n/3

1 Answer

+2 votes
by (51.1k points)
selected by
 
Best answer

Correct Answer is: (b) n

α = ω dω/dθ = - cω, where c is a constant.

or dω = - cdθ 

or  = ωi - cθ

For the first part,

ωi/ 2 = ωi - cθ or c(2πn) = ωi/ 2.

For the second part,

0 = ωi/ 2 - c(2πn') or n' = n.

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