[问答题]
A wheel of mass M has r(yl kruktof+ o8(d**tak kxo7xu hnt/ 3(+d5zndius R. It is standing 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 5z non x3d7uh (/k+ktxhas height h, where h