[问答题]
A wheel of mass M has radius R. It is standing vertical-ah 1jv fj;ro;j2o2 dxly onrbw mmzy4+9sao3 vf*2 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 (Figz3am +9rvm4w2 yo*fs b. 8–55). The step has height h, where h