[问答题]
A wheel of mass M has rpfm .t/y*tu5qf)y5bc adius R. It is standing t u8lyrvlslj,5u)/s* vertically on the floor, and we want to exert a horizontal force F at its axle so that it will climb a step against which it rests (Fig. 8–55) s)lul uj*5yt/lv,s r8. The step has height h, where h