题目内容
(18分)如图所示,一个质量为
的长木板静止在光滑的水平面上,并与半径为
的
光滑圆弧形固定轨道接触(但不粘连),木板的右端到竖直墙的距离为
;另一质量为2
的小滑块从轨道的最高点由静止开始下滑,从圆弧的最低点A滑上木板。设长木板每次与竖直墙的碰撞时间极短且无机械能损失。已知滑块与长木板间的动摩擦因数为
。试求
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/2014082500010988619200.png)
(1)滑块到达A点时对轨道的压力的大小
(2)若滑块不会滑离长木板,试讨论长木板与墙第一次碰撞前的速度
与
的关系
(3)若S足够大,为了使滑块不滑离长木板,板长
应满足什么条件
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825000109792337.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825000109808303.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825000109823303.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825000109839321.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825000109792337.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825000109870301.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/2014082500010988619200.png)
(1)滑块到达A点时对轨道的压力的大小
(2)若滑块不会滑离长木板,试讨论长木板与墙第一次碰撞前的速度
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825000109901265.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825000109839321.png)
(3)若S足够大,为了使滑块不滑离长木板,板长
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825000109932280.png)
(1)6mg;(2)若
,则木板与墙第一次碰前瞬间的速度为
;若
,则木板与墙第一次碰前瞬间的速度为![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825000110213308.png)
;(3)
。
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825000109964710.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825000109979732.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825000110198701.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825000110213308.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825000110244610.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825000110260537.png)
试题分析:(1)滑块从轨道的最高点到最低点,由机械能守恒,
设到达A点的速度为
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825000110276352.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825000110307885.png)
得:
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825000110322636.png)
由牛顿第二定律可知,在A点有:
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825000110338987.png)
由②③得:
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825000110369682.png)
由牛顿第三定律,滑块在A点对轨道的压力:
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825000110385724.png)
(2)若第一次碰撞前的瞬间,滑块与木板达到共同速度
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825000109901265.png)
则:
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825000110463751.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825000110478896.png)
由②⑥⑦得:
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825000110494691.png)
ⅰ.若
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825000109964710.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825000109979732.png)
ⅱ. 若
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825000110198701.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825000110213308.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825000110603894.png)
得:
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825000110213308.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825000110244610.png)
(3)因为S足够大,每次碰前滑块与木板共速;因为
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825000110728542.png)
由能量守恒得:
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825000110744973.png)
解得
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825000110260537.png)
评分标准:①⑥⑦每式2分,123分,其余每式1分。
![](http://thumb2018.1010pic.com/images/loading.gif)
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