The motor of an engine is erotating about its axis with an angular velocity of 100 rev/minute. It comes to rest in 15 s, after being switched off. Assumgn cnstant angular decelertion, calculate the number of revolutions made by it before coming to rest.

Explanation

Here, `omega_(0) = 100"rpm" = (100)/(60) xx 2pi = (10)/(3) rad//s`
`omega =0, t = 15 s`
From `omega = omega_(0) + alpha t`
`0 = (10pi)/(3) + alpha xx 15` or `alpha = (-10 pi)/(45)`
`alpha = (-2pi)/(9) rad//s^(2)`
Angular traced by the moton in the process is
`theta = omega_(0)t + (1)/(2)alpha t^(2) = (10pi)/(3) xx 15+ (1)/(2) ((-2pi)/(9)) (15)^(2) = 50pi - 25pi = 25pi`
`:.` No. of revolutions `= (theta)/(2pi) = (25pi)/(2pi) = 12.5`