[问答题]
A wheel of mass M has radius R. It is stand d jer )yrii, h;21f22aepg0rpaex +:ying vertically on the floor, and w3o. b/cba st7re want to exert a horizontal force F at its axle so that it will climb a . bab/c 37ortsstep against which it rests (Fig. 8–55). The step has height h, where h