Answer
(a) $\Delta \theta=69\ rev$
(b) $\Delta \theta=52\ rev$
Work Step by Step
(a) As $\Delta \theta=\frac{1}{2}(\omega_f+\omega_i)t$
We plug in the known values to obtain:
$\Delta \theta=\frac{1}{2}(0+0.96)(2.4min\times 60\frac{s}{min})$
$\Delta \theta=69\ rev$
(b) (As $\Delta \theta=\frac{1}{2}(\omega_f+\omega_i)t$
We plug in the known values to obtain:
$\Delta \theta=\frac{1}{2}(0.48+0.96)(1.2min\times 60\frac{s}{min})$
$\Delta \theta=52\ rev$