Halliday, Resnick & Walker — Rolling, Torque, and Angular Momentum: Problem 50

50 The rotor of an electric motor has rotational inertia \( I_m = 2.0 \times 10^{-3} \text{ kg}\cdot\text{m}^2 \) about its central axis. The motor is used to change the orientation of the space probe in which it is mounted. The motor axis is mounted along the central axis of the probe; the probe has rotational inertia \( I_p = 10 \text{ kg}\cdot\text{m}^2 \) about this axis. Calculate the number of revolutions of the rotor required to turn the probe through \( 30^\circ \) about its central axis.