[填空题]
A small 650-gram ball on the end of a thin, ligh 7sfw od5k88x0 9g7xebgh -fnst rod is rotwfvdn5 zl7f 91ated in a horizontal circle of radius 1.2 m. Calculat7f1wf5v 9z nlde (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. $m \cdot N$