[问答题]
A wheel of mass M has radiushd9em-a( ;yne 3twr8p R. )-w cns2v)gl )kiv.q1 mvuy)n It is standing 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 isiwn.cvmv- n)u) ) gy v12klq)t rests (Fig. 8–55). The step has height h, where h