[填空题]
(a) What is the angular momentum of a 2.8zngzwg4z.3 r/ sl9zh1 -kg uniform cylindrical grinding wheel xzs0 w6m,n+i 9bq/ hq/fhtud7ac0bi:+x3qyu of radius 18 cm when rotating ay ,9+/uhdhis3b t xmbqux67i0:q 0n/cf+w qzat 1500 rpm? $kg \cdot m^2$ (b) How much torque is required to stop it in 6.0 s? $m \cdot N$