Question

1. a) A fidget spinner is rotating at a certain angular velocity. As it began to slow down, it
took 45 seconds to stop with an average angular acceleration of 0.69 rads-2
. Calculate
the
(i) initial angular velocity in rpm.
(ii) number of revolution the spinner makes before it stops.

Answer 1

The angular acceleration is

$$\alpha=\frac{\omega_2-\omega_1}{t},\\\space\\ \omega_2=\alpha t+\omega_1=0.69\cdot45+0=45.69\text{ rad/s}.$$

The number of revolutions before it stopped is

$$n=\frac{\omega_2}{2\pi}=\frac{45.69}{2\pi}=7.272.$$