题目内容
如图,质量
的物体静止于水平地面的A处,A、B间距L=20m。用大小为30N,沿水平方向的外力拉此物体,经
拉至B处。(已知
,
。取
)
小题1:求物体与地面间的动摩擦因数μ;
小题2:用大小为30N,与水平方向成37°的力斜向上拉此物体,使物体从A处由静止开始运动并能到达B处,求该力作用的最短时间t。![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241304132188960.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824130413078570.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824130413109479.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824130413140653.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824130413156646.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824130413187664.png)
小题1:求物体与地面间的动摩擦因数μ;
小题2:用大小为30N,与水平方向成37°的力斜向上拉此物体,使物体从A处由静止开始运动并能到达B处,求该力作用的最短时间t。
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241304132188960.png)
小题1:0.5
小题2:
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241304132341714.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241304132652054.png)
(2)设
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824130413296302.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824130413328267.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824130413343283.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824130413328267.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824130413390305.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824130413421294.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241304134521186.png)
∴
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241304134842966.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241304134991024.png)
由于匀加速阶段的末速度即为匀减速阶段的初速度,因此有
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824130413530456.png)
∴
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824130413562884.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824130413593811.png)
∴
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241304136081656.png)
![](http://thumb2018.1010pic.com/images/loading.gif)
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