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 the equation, `0 = omega_(0) - alpha t`
`:. alpha=(omega_(0))/(t)=((100xx2pi)//60)/(15)=0.7 "rad s"^(-2)`
Now angle rotated before coming to rest, `theta = (omega_(0)^(2))/(2 alpha)`
or `theta =((100xx2pi//60)^(2))/(2xx0.7)=78.33` rad
or number rotations, `n=(theta)/(2pi)=12.5`.