[问答题]
A wheel of mass M has radius R. Ik 4b+,z:jr+ibxnw d(bt is standing vert2b;- rmtcph;r at(z- gically on the floor, and we want to exert a horizoct; - z(t;rh2 am-rbgpntal force F at its axle so that it will climb a step against which it rests (Fig. 8–55). The step has height h, where h