The motor of an engine is rotating about its axis with an angular velocity of 100 rev/minute. It comes to rest in 15 s, after being switched off. Assuming constant angular deceleration, calculate the number of revolutions 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`.