Question

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

Answer 1

$$\begin{array}{c}Time:\\ t=15s\\ =\frac{15}{60}min\\ =\frac{1}{4}min\\ \\ Angulardisplacement:\\ \theta =\left[\frac{\omega +{\omega }_o}{2}\right]t\\ =\left[\frac{0+100}{2}\right]\times \frac{1}{4}\\ =\frac{50}{4}\\ =12.5rotations\end{array}$$