Answer
a. $0.50 kg \cdot m^2$
b. $ 2.4 \times 10^{-2} N \cdot m$
Work Step by Step
a. Treat the ball like a point mass.
$$I=MR^2=(0.350 kg)(1.2m)^2\approx 0.50 kg \cdot m^2$$
b. The net torque is zero because the angular acceleration is zero, so the torque needed has the same magnitude as the torque caused by air friction.
(0.020 N)(1.2m) = $ 2.4 \times 10^{-2} N \cdot m$.