[填空题]
A small 650-gram ball on thes.v6brmx( yv9 end of a thin, light rod is rotat(zk1.khmvn 5t ed in a horizontal circle of radinz(v1ktm5 h. kus 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. $m \cdot N$