[问答题]
A wheel of mass M has radius R. It( fa,v6es2 ros8o nnn0 is standing verti7;f :d,qrph wycally on the floor, and we want to exert a horizontal force F at its axle so that it will c d:hp; wqr,y7flimb a step against which it rests (Fig. 8–55). The step has height h, where h
