题目内容
如图所示,MPQ为竖直面内一固定轨道,MP是半径为R的1/4光滑圆弧轨道,它与水平轨道PQ相切于P,Q端固定一竖直挡板,PQ长为s。一质量为m的小物块在M端由静止开始沿轨道下滑,与挡板发生一次碰撞(碰撞无机械能损失)后停在距Q点为L的地方,重力加速度为g,不计空气阻力。求:
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408242122170992328.jpg)
(1)物块滑至圆弧轨道P点时轨道对物块的支持力大小;
(2)物块与PQ段动摩擦因数μ。
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408242122170992328.jpg)
(1)物块滑至圆弧轨道P点时轨道对物块的支持力大小;
(2)物块与PQ段动摩擦因数μ。
(1)
(2)
或者![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824212218924643.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824212217286614.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824212218066578.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824212218924643.png)
试题分析:(1)从M到P,由动能定理:
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824212219704784.png)
在P点:
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824212220515858.png)
得:
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824212217286614.png)
(2)第一种情况:物块与Q处的竖直挡板相撞后,向左运动一段距离,停在距Q为L的地方。根据动能定理有:
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824212221295866.png)
得:
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824212218066578.png)
第二种情况:物块与Q处的竖直挡板相撞后,向左运动冲上圆弧轨道后,返回水平轨道,停在距Q为L的地方。根据动能定理有:
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824212223292902.png)
得:
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824212218924643.png)
点评:本题考查了利用动能定理解决实际问题的能力,有一定综合性。
![](http://thumb2018.1010pic.com/images/loading.gif)
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