[填空题]
A small 650-gram ball on the end of a thin, light rod is rotgw2yhj2u jop,5.im, foj.4 ez ated in a w tooltld 91vb4(jx/,x6 0d8ivr se(rhorizontal circle of rv,ed/ ti8x r l9 o1jo(6 4xlbw(tdvsr0adius 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. $m \cdot N$