题目内容
(12分)如图所示,一长为L的长方形木块在水平地面上由静止开始以加速度a做匀加速直线运动,先后经过A、B两点位置,且通过A、B两点所用的时间分别为t1和t2,求:
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/2014082500261182513012.jpg)
⑴木块分别通过位置A、B的平均速度大小;
⑵木块前端P点到达位置A时的瞬时速度;
⑶木块前端P在A、B之间运动所需的时间。
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/2014082500261182513012.jpg)
⑴木块分别通过位置A、B的平均速度大小;
⑵木块前端P点到达位置A时的瞬时速度;
⑶木块前端P在A、B之间运动所需的时间。
⑴
=
,
=
;⑵vA=
-
;⑶t=
(
-
)+![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825002611997528.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825002611856345.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825002611872388.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825002611888344.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825002611903429.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825002611872388.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825002611934488.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825002611950378.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825002611966372.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825002611981342.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825002611997528.png)
试题分析:⑴根据平均速度定义式
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825002612028270.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825002612044354.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825002611856345.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825002611872388.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825002611888344.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825002611903429.png)
⑵根据匀变速直线运动平均速度等于中点时刻速度可知,木块前端P点通过A点后
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825002612122405.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825002611856345.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825002611856345.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825002611934488.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825002611872388.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825002611934488.png)
⑶同理,木块前端P点通过B点后
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825002612215440.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825002611888344.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825002611888344.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825002612246521.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825002611903429.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825002612246521.png)
根据匀变速直线运动速度公式可知,木块前端P在A、B之间运动所需的时间为:t=
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825002612293556.png)
解得t=
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825002611950378.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825002611966372.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825002611981342.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825002611997528.png)
![](http://thumb2018.1010pic.com/images/loading.gif)
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