The motor of an engine is rotating about its axis with an angular velocity of 100 rpm. It comes to rest in 15 s after being switched off. Assuming constant angular deceleration, calculate the number of revolution made by it before coming to rest.

Options

A. `12.5`
B. 40
C. `32.6`
D. `15.6`

Answer

A

Explanation

From equation of motion (angular),
`0=omega_(0)-alphatrArralpha=(omega_(0))/(t)=((100xx2pi)//60)/(15)=0.69"rad s"^(-2)`
Now, angle rotated before coming to rest is given by
`theta=(omega_(0)^(2))/(2alpha)=((100xx2pi)/(60))^(2)/(2xx0.7)=78.25rad`
`therefore" Number of revolutions"=(theta)/(2pi)=12.5`