[问答题]
A wheel of mass M has radius R. It is js36tvjshy. +ra 4c7estanding vertically zc;nmhl4w *.hex ;yn1 on the floor, and we want to exert a horizontal force F at its axle so that it wille*1.c h;n4xnmlz;w yh climb a step against which it rests (Fig. 8–55). The step has height h, where h