如图所示,有一光滑的半径可变的圆形轨道处于竖直平面内,圆心O

如图所示,有一光滑的半径可变的圆形轨道处于竖直平面内,圆心O点离地高度为H.现调节轨道半径,让一可视为质点的小球a从与O点等高的轨道最高点由静止沿轨道下落,使小球离开轨道后运动的水平位移S最大,则小球脱离轨道最低点时的速度大小应为

(A)          

(B)

(C)        

(D)

答案

A

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