题目内容
木块长为L,静止在光滑的水平桌面上,有A、B两颗规格不同的子弹以速度相反的VA、VB同时射向木块,A、B在木块中嵌入的深度分别为dA、dB,且dA>dB,(dA+dB)<L,木块一直保持静止,如图所示,则由此判断子弹A、B在射入前:
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241743291923583.jpg)
A.速度![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824174329223492.png)
B.子弹A的动能等于子弹B的动能
C.子弹A的动量大小大于子弹B的动量大小
D.子弹A的动量大小等于子弹B的动量大小
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241743291923583.jpg)
A.速度
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824174329223492.png)
B.子弹A的动能等于子弹B的动能
C.子弹A的动量大小大于子弹B的动量大小
D.子弹A的动量大小等于子弹B的动量大小
AD
试题分析:由于木块始终保持静止状态,则两子弹对木块的推力大小相等,则两子弹所受的阻力大小相等,设为f,根据动能定理得:对A子弹:
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824174329535706.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824174329785641.png)
对B子弹::
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824174330159709.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824174330409652.png)
由于
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824174330659521.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824174330971570.png)
对两子弹和木块组成的系统动量守恒,则有
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824174331485891.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824174331766576.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824174332187519.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824174332484753.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824174332780487.png)
故选AD
点评:本题运用动能定理和动量守恒定律研究冲击块模型,分析木块处于静止状态,确定出两子弹所受的阻力大小相等是基础.
![](http://thumb2018.1010pic.com/images/loading.gif)
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