A pulley, with a rotational inertia of 4.6 × 10-3 kg m2 about its axle and a radius of 7.0 cm, is acted on by a force applied tangentially at its rim. The force magnitude varies in time as F = 0.34t + 0.27t2, where F is in newtons if t is given in seconds. The pulley is initially at rest. At t = 3.1s what is its angular acceleration?