[填空题]
A small 650-gram ball on the end of a thin, light rod is rotatedv)4 pa(9broe f in a hor0 +c i:2gvle;zdx9lcq izontal circle of radius 1.2 z:9 ce vgx0lcl2 q+d;im. 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. $m \cdot N$