[问答题]
A wheel of mass M has radius R. It is standingztg+ns/ mw ;dx p4xnb.h6f(l+b8 0seo vertically on the fl7le1u+ no z:rxoor, and we want to exert a horizontal force F at its axle so that it wiexo17 l nr+:uzll climb a step against which it rests (Fig. 8–55). The step has height h, where h