The motor of an engine is rotating about its axis with angular velocity of `120` r.p.m. it comes to rest in `10s`, after being switched off. Assuming constant deceleration, calculate the number of revolutions made by it before coming to rest.

Explanation

Here, `omega_(0)=120` r.p.m `=2` r.p.s `=4pirads^(-1)`
`omega=0` and `t=10s` `omega=omega_(0)+at`
`0=4pi+axx10` or `a=-0.4pirads^(-2)`
Also, the angle covered by the motor,
`theta=omega_(0)t+(1)/(2)at^(2)`
`:. theta=4pixx10+(1)/(2)xx(-0.4pi)xx10^(2)=40pi-20pi`
`=20pi`rad
Hence, the number of revoluations completed
`n=(theta)/(2pi)=(20pi)/(2pi)=10`