题目内容
在均匀介质中选取平衡位置在同一直线上的9个质点,相邻两质点的距离均为
,如图11(a)所示,一列横波沿该直线向右传播,
时到达质点1,质点1开始向下运动,经过时间
第一次出现如图(b)所示的波形.则该波的周期为 ,波速为 。 ![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241249489614522.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824124948712290.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824124948727370.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824124948759385.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241249489614522.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824124949024574.png)
分析:由图确定波长,t=0时到达质点1,质点1开始向下运动,则介质中所有质点起振方向均向下.图b中质点9此刻振动方向向上,说明波不是才传到质点9,而是传到9后又经过了
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824124949055338.png)
解:横波沿该直线向右传播,图示时刻质点9的振动方向向上.由题波源1的起振动方向向下,则第一次出现如图(b)所示的波形,振动传到质点9后,又传播了
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824124949055338.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824124949102382.png)
由图读出波长λ=8L,则波速v=
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824124949117427.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824124949133513.png)
故本题答案是:
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824124949024574.png)
![](http://thumb2018.1010pic.com/images/loading.gif)
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