题目内容
(2012年2月山东潍坊重点中学联考)如图所示,用内壁光滑的薄壁细管弯成的“S”形轨道固定于竖直平面内,弯曲部分是由两个半径均为R =" 0.2" m 的半圆平滑对接而成(圆的半径远大于细管内径).轨道底端A与水平地面相切,顶端与一个长为l =" 0.9" m的水平轨道相切B点.一倾角为θ = 37°的倾斜轨道固定于右侧地面上,其顶点D与水平轨道的高度差为h =" 0.45" m,并与其它两个轨道处于同一竖直平面内.一质量为m =" 0.1" kg 的小物体(可视为质点)在A点被弹射入“S”形轨道内,沿轨道ABC运动,并恰好从D点以平行斜面的速度进入斜轨道.小物体与BC段间的动摩擦因数μ = 0.5. (不计空气阻力,g取10 m/s2.sin37°= 0.6,cos37°=" 0.8)"
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/2014082413265819015257.png)
(1)小物体从B点运动到D点所用的时间;
(2)小物体运动到B点时对“S”形轨道的作用力大小和方向;
(3)小物体在A点的动能.
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/2014082413265819015257.png)
(1)小物体从B点运动到D点所用的时间;
(2)小物体运动到B点时对“S”形轨道的作用力大小和方向;
(3)小物体在A点的动能.
(1)
(2) 11.5N(3) ![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824132658361691.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824132658221640.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824132658361691.png)
(1)物块从C到D做平抛运动,
①
② 解得:
③
④
物体从B到C做匀减速运动,由牛顿第二定律得
⑤
⑥
⑦
解得:
⑧
(2)物体运动到B点受到向下的弹力,由牛顿第二定律得:
⑨
由牛顿第三定律
⑩
向上的压力,大小为11.5N (11)
(3)从A到B的过程有机械能守恒得
(12)
(13)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824132658564671.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824132658720730.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824132658767607.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824132658923521.png)
物体从B到C做匀减速运动,由牛顿第二定律得
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824132658954581.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824132659032676.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824132659079593.png)
解得:
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824132658221640.png)
(2)物体运动到B点受到向下的弹力,由牛顿第二定律得:
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824132659578960.png)
由牛顿第三定律
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824132659734539.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824132659781710.png)
(3)从A到B的过程有机械能守恒得
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241326598121097.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824132658361691.png)
![](http://thumb2018.1010pic.com/images/loading.gif)
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