题目内容
(10分)如图所示,平台离水平地面的高度为H=5m,一质量为m=1kg的小球从平台上A点以某一速度水平抛出,测得其运动到B点时的速度为vB=10m/s。已知B点离地面的高度为h=1.8m,取重力加速度g=10m/s2,
以水平地面为零势能面。问:
(1)小球从A点抛出时的机械能为多大?
(2)小球从A点抛出时的初速度v0为多大?
(3)B点离竖直墙壁的水平距离L为多大?![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241245145415024.jpg)
以水平地面为零势能面。问:
(1)小球从A点抛出时的机械能为多大?
(2)小球从A点抛出时的初速度v0为多大?
|
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241245145415024.jpg)
(10分) 解:(1)由机械能守恒定律得,A点时的机械能
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/2014082412451455773.gif)
2分
代入数据解得,
1分
(2)
或
2分
代入可解得
2分
另解
,
或
2分
代入可解得
1分
把小球到达B点时的速度进行正效分解,如图所示
由图可得,
1分
(3)
1分
1分
综合可解得
1分
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/2014082412451455773.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824124514572743.gif)
代入数据解得,
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824124514588436.gif)
(2)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824124514604803.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824124514604833.gif)
代入可解得
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824124514619434.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824124514635789.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824124514650538.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824124514666385.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824124514682543.gif)
代入可解得
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824124514682433.gif)
把小球到达B点时的速度进行正效分解,如图所示
由图可得,
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824124514697616.gif)
(3)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824124514713294.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824124514728796.gif)
综合可解得
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824124514760414.gif)
略
![](http://thumb2018.1010pic.com/images/loading.gif)
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