题目内容
如图所示,质量为M的金属块放在水平地面上,在与水平方向成θ角斜向上、大小为F的拉力作用下,由静止开始向右做加速度为a的匀加速直线运动,重力加速度为g。求:
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241146414313429.jpg)
(1)金属块与地面间的动摩擦因数;
(2)经过时间t撤去拉力F,求撤去拉力后金属块在地面上滑行的时间.
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241146414313429.jpg)
(1)金属块与地面间的动摩擦因数;
(2)经过时间t撤去拉力F,求撤去拉力后金属块在地面上滑行的时间.
(1)
(2)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824114641446821.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824114641462975.gif)
(1)分析物体受力如图,由牛顿第二定律得:
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241146414771657.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241146414931230.gif)
①
②
③
联立①②③解得:
④
(2)撤去拉力F后,物体受力如图,设物体滑行的时间为t1,由动量定理得:
⑤
由匀变速运动公式:
⑥
联立④⑤⑥解得:
⑦
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241146414771657.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241146414931230.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824114641509549.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824114641524582.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824114641524398.gif)
联立①②③解得:
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824114641446821.gif)
(2)撤去拉力F后,物体受力如图,设物体滑行的时间为t1,由动量定理得:
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824114641555572.gif)
由匀变速运动公式:
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824114641587351.gif)
联立④⑤⑥解得:
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824114641462975.gif)
![](http://thumb2018.1010pic.com/images/loading.gif)
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