Question

A wheel has a speed of 1200 revolutions per minute and is made to slow down at a rate of $4radians/s^2$ The number of revolutions it makes before coming to rest is

• A. 143
• B. 272
• C. 314
• D. 722

Answer 1

Answer: (C)

314

Answer 2

$\omega_i = 2 \pi \left[ \frac{1200}{60} \right] = (40 \pi) rad \, s^{-1}$ $\omega_f = 0$ $\alpha = 4r ad\,s^{-2}$ $\theta = \frac{\omega^2_f - \omega^2_i}{2 \alpha} = ( 200 \pi )^2 \, rad$ number ofrotations made = $\frac{\omega}{2 \pi} = 100 \pi = 314$