题目内容
两个物块A、B的质量均为m,叠放在一个竖直的弹簧上,如图所示,弹簧的劲度系数为
,弹簧的质量忽略不计,今用一竖直向下的力F压物块A,弹簧在F的作用下又缩短了
(弹簧仍在弹性限度内),突然撤去外力F,此时A对B的作用力的大小为
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241232411221290.png)
A.F B.F+mg C.
D.![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824123241185841.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824123240966320.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824123241060391.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241232411221290.png)
A.F B.F+mg C.
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824123241154797.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824123241185841.png)
C
撤去外力F,因为弹簧的弹力不能突变,所以以整体为研究对象可知,合外力跟力F等大反向,即大小为F=K
,方向向上,则有:
,对A有:
,两物体加速度相等,所以可得此时A对B的作用力的大小N=![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824123241154797.png)
故选C
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824123241060391.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824123241232642.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824123241263655.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824123241154797.png)
故选C
![](http://thumb2018.1010pic.com/images/loading.gif)
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