[填空题]
Calculate the net torque about tue *:;* (kvv nyll j;n39hyzjhhe axle of the wheel showih9+ca :;r uufz 0+fx s m;smrm+mnqv4t88 3mhn in Fig. 8–39. Assume that a friction torque of 0.4st;mrm cvi0zh 3 ;uqm+axnfsrhf + m+884mu 9: $m \cdot N$ opposes the motion. $m \cdot N$