[填空题]
(a) What is the angular momentum of a 2.8-kg uniform cylindricay)7c2fk70g v8xozb znl grid6i 59khv92 om;muvb3 hng2jxnding wheel of radius 18 cm when rotati9uim 6 xjo2vb3h kn9gd;vhm25ng at 1500 rpm? $kg \cdot m^2$ (b) How much torque is required to stop it in 6.0 s? $m \cdot N$