[问答题]
A wheel of mass M has radiusju5czb7)+ xt3 ; srszs R.tdrcf.3r + h+k 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 it rests (Fig. 8–55). The ch3. td+krr+f step has height h, where h