题目内容
如图所示,水平固定倾角为
的光滑斜面上有两质量均为m的小球A、B,它们用劲度系数为k的轻质弹簧连接,现对B施加一水平向左推力F使A、B均静止在斜面上,此时弹簧的长度为l,则弹簧原长和推力F的大小分别为( )
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241515354296876.png)
A.
B.![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241515359431577.png)
C.![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241515360371649.png)
D.![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241515361151494.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824151535226405.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241515354296876.png)
A.
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241515356781614.png)
B.
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241515359431577.png)
C.
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241515360371649.png)
D.
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241515361151494.png)
D
试题分析:对于连接体问题,优先考虑以整体为研究对象,本题中以整体为研究对象,可以求出力F的大小,然后根据A处于平衡状态,可以求出弹簧弹力,从而进一步求出弹簧的原长。
以整体为研究对象,系统处于平衡状态,沿斜面方向有:
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824151536240944.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824151536318823.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824151536427790.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824151536552464.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824151536645802.png)
故选D
点评:对于连接体问题注意整体与隔离法的应用,正确选取研究对象然后受力分析,根据所处状态列方程求解.
![](http://thumb2018.1010pic.com/images/loading.gif)
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