[问答题]
A wheel of mass M has radius R. It s9 thgi;pj-e i2odzlvla(h /:bcg ;.58blr whe3n3t6is standing vertically on the floor, and we want to exert a nrb8wth36l 3e horizontal 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