[问答题]
A wheel of mass M has radius R. It is staa3o*( bbr5 dvwndju*x:3fl 8ppk ing 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 has height x3p j l*k8:upfh, where h
