题目内容
射箭的弓顶部跨度为l,弦均匀且弹性良好,其自由长度为l,发射时弦和箭可等效为右图乙的情景,假设弓的跨度保持不变.已知弦的劲度系数为k,发射箭时弦的最大长度为
(弹性限度内),则箭被发射瞬间所受的最大弹力为(设弦的弹力满足胡克定律)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241401275023211.jpg)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824140127424436.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241401275023211.jpg)
A.![]() | B.![]() | C.![]() | D.![]() |
B
本题考查的是胡克定律问题,由于弦拉伸时弦上各点张力相等,
现在弦伸长了
,箭左端两侧的力均为
,将两个力在水平方向上投影,
,B正确;
现在弦伸长了
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824140127814465.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824140128001524.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241401282041317.png)
![](http://thumb2018.1010pic.com/images/loading.gif)
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