题目内容
(9分)如图13所示,悬挂的直杆
长为
,在其下
处,有一长为
的无底圆筒
,若将悬线剪断,直杆能穿过圆筒。空气阻力不计,重力加速度为g。求:
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241531033969551.png)
(1)从悬线剪断至直杆B端到达圆筒上端所用的时间;
(2)直杆穿过圆筒所用的时间。
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824153100760396.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824153100900313.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824153100978341.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824153101150350.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824153101275405.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241531033969551.png)
(1)从悬线剪断至直杆B端到达圆筒上端所用的时间;
(2)直杆穿过圆筒所用的时间。
(1)
(2)
=
-
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824153103459718.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824153103615529.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824153103740909.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824153103849604.png)
试题分析:(1)设直杆
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824153103974309.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824153104332313.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824153104691291.png)
由
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824153104847650.png)
L2=h
得:
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824153103459718.png)
(2) 直杆穿过圆筒所用的时间是从杆
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824153103974309.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824153104332313.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824153105253300.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824153105534315.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824153105253300.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824153105534315.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824153105705327.png)
则
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824153106064987.png)
所以
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824153103615529.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824153103740909.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824153103849604.png)
点评:难度中等,对于这种多过程问题,要能够把整段过程分解为独立的分过程,对各个分过程分析运动和受力,利用相关公式求解
![](http://thumb2018.1010pic.com/images/loading.gif)
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