[填空题]
(a) What is the angular momentum of a 2.8-kg uniform cylindrical gri e0p*,ab ld4iinding wy 6ny;jpz9 k3 p-t1qtdheel of radius 18 cm when rotating at 1;ntk39p p-d16q y tyjz500 rpm? $kg \cdot m^2$
(b) How much torque is required to stop it in 6.0 s? $m \cdot N$