19. In the right figure, what magnitude of the force F applied horizontally at the axle of the wheel is necessary to raise the wheel over an obstacle of height h? The wheel's radius is r and its mass is m.

(A)\( \frac{\sqrt{2rh-h^2}}{r+h}mg \)

(B)\( \frac{\sqrt{2rh-h^2}}{r-h}mg \)

(C)\( \frac{\sqrt{2rh+h^2}}{r-h}mg \)

(D)\( \frac{2\sqrt{2rh-h^2}}{r-h}mg \)

(E)\( \frac{\sqrt{2rh+h^2}}{r+h}mg \)

答案：登入後查看
統計： 尚無統計資料