题目:
如图质量为m的小球,从离桌面高H处由静止下落,桌面离地面高为h,设桌面处物体重力势能为零,空气阻力不计,那么,小球落地时的机械能为( )
A.mgh
B.mgH
C.mg(H+h)
D.mg(H-h)
答案:
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