[问答题]
A wheel of mass M has radius R. It is standing vertically on th/d 0kpflugm3p.50rd d e floor, and we :n hog)*uhjp4 want to exert a horizontal force F at its axle so that it will climb a step against which it rests (Fig. 8–55). The step has height h, where )jnghup:h o 4*h