[填空题]
A small 650-gram balp1b+ 6sizbeic5n2l9x l on the end of a u btj68t 51qrathin, light rod is rotated in a horizontal circle of r t168artjqbu 5adius 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. $m \cdot N$