A Buddhist monk is holding a hand-held prayer wheel. A small metal ball of 0.20 kg is attached to the head of the prayer wheel by a string of length 0.19 m. The monk starts to move the prayer wheel which makes the metal ball move in a horizontal circle, accelerating it to a rotational speed of 66 rpm in 5.5 s from rest. Determine the magnitude and origin of the torque on the small ball.