如图所示，长木板固定于水平实验台上。放置在长木板
处的小球(大小不计)，在水平恒力的作用下向右运动，运动到长木板边缘
处撤去水平恒力，小球水平抛出后恰好落在光滑斜面顶端
处，且速度方向平行于斜面。己知小球质量为
，与水平长木板间的动摩擦因数为
，长木板
长为
，距离水平地面的高度为
，斜面倾角为
、
、
两点间竖直高度为
。求：
(1)
的水平距离
；
(2)水平恒力
的大小；
(3)小球落地时速度
的小。
（1）
（2）
（3）
（1）小球落在
处时，
············································· 2分
·································································· 2分
小球从
到
···················································································· 2分
··················································· 2分
（2）小球从
到
由动能定理得；
·········································································· 3分
······································································ 2分
（3）小球从到地，机械能守恒得：
······································································· 3分
······································································ 2分
（其他正确解法同样得分）