题目内容
在一次消防演习中,质量为60kg的消防员欲到达距离楼顶l=40m处的房间。如图所示,他沿一条竖直悬垂的轻绳从静止开始匀加速下滑,当他滑到该房间的窗户A处时,突然停止下滑,同时用脚踢开窗户,自己反弹了一下,然后进入窗内。已知消防员从开始下滑到刚进入窗内共用了时间t=10s,试估算他沿绳子下滑时受到的摩擦力f大小最接近( )
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241519423301470.jpg)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241519423301470.jpg)
A.100N | B.300N | C.600N | D.900N |
B
试题分析:消防员先加速下滑,然后做单摆运动,总时间为10s,而运动员做单摆运动的周期为
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824151942346846.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824151942455681.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824151942564561.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824151942674652.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824151942720633.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824151942814604.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824151943048619.png)
点评:做本题的关键一定要清楚消防员的 运动过程分为两个过程,一是匀加速下滑过程,一是单摆运动,
![](http://thumb2018.1010pic.com/images/loading.gif)
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