[问答题]
A wheel of mass M has radius R. It is standing ipwyg:t0/ f+(j2 s kwyvertically on the floor, and we u2axti2:8wgsg 9m-ocxqi w2ij ,/s,nwant to exert a horizontal force F at its axle so that it will climb a step against which it rests (Fig. 8–55). The step h/2tjx 9uani-si 82ixc: 2 ,swg m,woqgas height h, where h