[填空题]
(a) What is the angular momentum of a 2.8-kg uniformpn1k3zkt 0 ei*s4r vb+ cylindriv(ftd/jpa4+)z dlx2x cal grinding wheel of radius 18 cm when rotating at 2 4d+vjtalxfd)pz/ (x 1500 rpm? $kg \cdot m^2$ (b) How much torque is required to stop it in 6.0 s? $m \cdot N$