题目内容
如图所示的装置中,水平放置的轻弹簧A.B.C原长相同,劲度系数分别为k、2k、3k,物体D放在光滑的水平面上处于平衡。要使物体D由平衡位置向右移动距离x,求所施外力的大小和方向。
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241156499721517.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241156499721517.gif)
F=
,方向向右
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241156501131029.gif)
设物体D处于平衡位置时,受拉力TC和TB,TC=TB,弹簧A的拉力TA=TB。当D在外力F作用下向右移动距离x,拉力TC减小了3kx。弹簧A.B的伸长量分别增加了x1、x2,有x1+x2=x,kx1=2kx2。解得x1=
,如图所示, x2=
。物体处于平衡, F+TC-3kx=TB+
,得外力F=
,方向向右。
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241156502372165.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824115650128990.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824115650144986.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241156501911017.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241156501131029.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241156502372165.gif)
![](http://thumb2018.1010pic.com/images/loading.gif)
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