题目内容
如图所示,劲度系数为k的轻弹簧一端固定在墙上,另一端与置于水平面上质量为m的物体接触(未连接),弹簧水平且无形变。用水平力F缓慢推动物体,在弹性限度内弹簧长度被压缩了x0 ,此时物体静止。撤去F后,物体开始向左运动,运动的最大距离为4x0。物体与水平面间的动摩擦因数为μ,重力加速度为g 。则( )
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408242019437953206.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408242019437953206.png)
A.撤去F时,物体的加速度大小为![]() |
B.撤去F后,物体先做加速运动,再做减速运动 |
C.物体做匀减速运动的时间为![]() |
D.物体在加速过程中克服摩擦力做的功为![]() |
ABD
试题分析:撤去F后,在物体离开弹簧的过程中,弹簧弹力是变力,由受力分析可知,物体先做加速度减小的加速运动,当弹簧弹力减小到与滑动摩擦力相等时,速度达到最大,然后做加速度反向增大的减速运动,随即离弹簧再做匀减速运动直至停止。也即经历了变加速、变减速、匀减速三种运动情况,当撤去推力F的瞬间,由牛顿第二定律可知
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408242019480541112.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824201948693788.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824201949286754.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824201950316782.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408242019513301086.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824201952312838.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824201953420643.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824201953420643.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824201955698903.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408242019568051359.png)
点评:本题难度较大,解答该题的关键在于做好受力分析,识别运动过程以及找准平衡位置。由于弹簧的力是变力,分析物体得运动过程,增加了难度
![](http://thumb2018.1010pic.com/images/loading.gif)
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