# Answer on Mechanics | Relativity Question for rksingh

Question #20229

a ceiling fan rotating at its full speed of 1200rpm is swithched off at t =0 .it cums at rest at t=5 s assuming uniform motion ,the no. of revolution made by it b4 cuming to rest ??

Expert's answer

Equation of motion is

f = wt-et^2/2

where f is number of revolutions, t is time, w is initialrotation speed and e is angular deceleration.

it is obvious that e = w/(1/12 of minute) = 14400minute^(-2)

Hence

f = 1200t-14400t^2/2, t=1/12 of minute = 5 sec.

f = 100-50 = 50 revolutions will be done.

f = wt-et^2/2

where f is number of revolutions, t is time, w is initialrotation speed and e is angular deceleration.

it is obvious that e = w/(1/12 of minute) = 14400minute^(-2)

Hence

f = 1200t-14400t^2/2, t=1/12 of minute = 5 sec.

f = 100-50 = 50 revolutions will be done.

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