题目内容
如图所示,风洞实验室中能模拟产生恒定向右的风力。质量
的小球穿在长
的直杆上并置于实验室中,球与杆间的动摩擦因数为0.5,当杆竖直固定放置时,小球恰好能匀速下滑。保持风力不变,改变固定杆与竖直线的夹角
,将小球从O点静止释放。g取10m/s2,
,
,求:
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/201408250045535121500.png)
(1)小球受到的风力大小;
(2)当
时,小球离开杆时的动能。
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825004553418545.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825004553434492.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825004553449479.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825004553465646.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825004553465653.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/201408250045535121500.png)
(1)小球受到的风力大小;
(2)当
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825004553449479.png)
(1)
;(2)1.8J
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825004553527511.png)
试题分析:(1)当杆竖直固定放置时,
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825004553543586.png)
解得:
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825004553527511.png)
(2)当
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825004553449479.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/201408250045535901861.jpg)
垂直杆方向上有:
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/201408250045536051039.png)
得:
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825004553636575.png)
小球受摩擦力
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825004553652822.png)
小球沿杆运动的加速度为
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/201408250045536681476.png)
由
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825004553683664.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825004553699580.png)
球离开杆时的动能为
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825004553730936.png)
![](http://thumb2018.1010pic.com/images/loading.gif)
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