[问答题]
A wheel of mass M has radius R. It is standing vertica+vva1* g *0lbba .rdc awhc0le97jg)u lly on the floor1iwa-(i /wkk7szj : qm, and we want to exert a horizontal force F at its axle so that it will climb a step aga1(k-z:/ 7sw mwiikjqainst which it rests (Fig. 8–55). The step has height h, where h