Question

A wheel is rotating at $900\,\,rpm$ about its axis. When the power is cut off it comes to rest in $1\min$ . The angular retardation in $rad/{{s}^{2}}$ is

• A. $\pi /3$
• B. $\pi /2$
• C. $\pi /6$
• D. $\pi /8$

Answer 1

Answer: (B)

$\pi /2$

Answer 2

$n=900\, rpm =\frac{900}{60} rps =15 rps$ $\therefore t=1\, \min =60\, s$ From equation of angular motion, we have $\omega=\omega_{0}-\alpha t$ $\therefore \omega=2 \pi n-\alpha t$ $\Rightarrow 0=2 \pi(15)-\alpha(60)$ $\Rightarrow \alpha=\frac{30 \pi}{60}=\frac{\pi}{2} rad / s ^{2}$