题目内容
如图3-2-2所示,一弹簧自由端未悬挂重物时指针正对刻度5,在弹性限度内,挂上80 N的重物时指针正对刻度45.若指针正对20,所挂重物是( )
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824120407927686.jpg)
图3-2-2 图3-2-3
A.40 N | B.30 N |
C.20 N | D.因不知弹簧的劲度系数,无法计算 |
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241204079121292.jpg)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824120407927686.jpg)
图3-2-2 图3-2-3
B
设劲度系数为k,则k(45-5)=80,F=k(20-5),解得F="30" N,B项正确.
![](http://thumb2018.1010pic.com/images/loading.gif)
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