Given: Initial angular speed, $\omega_0 = 1200 \text{ rpm} = \frac{1200 \times 2\pi}{60} \text{ rad/s} = 40\pi \text{ rad/s}$. Final angular speed, $\omega = 3120 \text{ rpm} = \frac{3120 \times 2\pi}{60} \text{ rad/s} = 104\pi \text{ rad/s}$. Time taken, $t = 16 \text{ s}$.

Using the first equation of rotational kinematics: $\omega = \omega_0 + \alpha t$ $\alpha = \frac{\omega - \omega_0}{t}$ $\alpha = \frac{104\pi - 40\pi}{16}$ $\alpha = \frac{64\pi}{16} = 4\pi \text{ rad/s}^2$.