[填空题]
A small 650-gram ball on the end of a t+jatdf)f 7wq +hin, l zl59yrbn r :rlc2b8b/ight rod is rotated in a horizontal circle of radlbr:2cb5/z r9 nr yb8lius 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. $m \cdot N$