[填空题]
A small 650-gram ball o s5:xto2dga +tn the end of a thin, light rod is rotated isqoe 466t*k8vvqdci4 n a horizontal circl8 vi t6dsv64qoe4k*cq e of radius 1.2 m. Calculate (a) the moment of inertia of the ball about the center of the circle, $kg \cdot m^2$ (b) the torque needed to keep the ball rotating at constant angular velocity if air resistance exerts a force of 0.020 N on the ball. Ignore the rod’s moment of inertia and air resistance. $m \cdot N$