[问答题]
A wheel of mass M has radius R. It is stam/ nsv 7;ab(ufnding0pk5eu gbp 4(b 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 (b 0g5ekppb4u h, where h