[问答题]
A wheel of mass M has radius R. It is stapm6zq vxd .o+0nylj ;8; lieoa(qzs *;brpy)j+ding 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 step haq r;ya+)p l8ozb s;yj;* (iejls height h, where h