题目内容
用劲度系数k=500N/m的轻弹簧,水平拉一木板使它沿水平桌面做匀速直线运动,弹簧长度L1=12cm.若在木板上加一个质量m=5kg的铁块,仍用原弹簧拉住它沿水平桌面做匀速直线运动,弹簧的长度L2=14cm,则木板与水平桌面间的动摩擦因数为多少?(g取10m/s2)
0.2
设木板的质量为M,则开始时,
①
后来加上铁块后,
②
联立①②得,![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824115329980342.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824115329995323.gif)
代入数据得,![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824115330167166.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824115329949307.gif)
后来加上铁块后,
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824115329964314.gif)
联立①②得,
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824115329980342.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824115329995323.gif)
代入数据得,
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824115330167166.gif)
![](http://thumb2018.1010pic.com/images/loading.gif)
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