Answer
$t=2.9\ s$
Work Step by Step
(a) We know that
$\theta=\frac{\omega_f2-\omega_i^2}{2\alpha}$
We plug in the known values to obtain:
$\theta=\frac{(6.3)^2-(0)^2}{2(2.2)}$
$\theta=9.0rad\times 1\frac{rev}{2\pi \space rad}=1.4rev$
(b) As $\alpha=\frac{\omega_f-\omega_i}{t}$
$\implies t=\frac{\omega_f^2-\omega_i^2}{\alpha}$
We plug in the known values to obtain:
$t=\frac{6.3-0}{2.2}=2.9\ s$
