题目内容
如图所示,已知倾角为θ=45°、高为h的斜面固定在水平地面上.一小球从高为H(h<H<
)处自由下落,与斜面做无能量损失的碰撞后水平抛出.小球自由下落的落点距斜面左侧的水平距离x满足一定条件时,小球能直接落到水平地面上.
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/201408250045565382127.png)
⑴求小球落到地面上的速度大小;
⑵求要使小球做平抛运动后能直接落到水平地面上,x应满足的条件;
⑶在满足⑵的条件下,求小球运动的最长时间.
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825004556507472.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/201408250045565382127.png)
⑴求小球落到地面上的速度大小;
⑵求要使小球做平抛运动后能直接落到水平地面上,x应满足的条件;
⑶在满足⑵的条件下,求小球运动的最长时间.
⑴
;⑵
;⑶![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825004556600754.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825004556554584.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825004556585752.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825004556600754.png)
试题分析:⑴设小球落到底面的速度为v
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825004556616779.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825004556554584.png)
⑵小球做自由落体的末速度为
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825004556647911.png)
小球做平抛运动的时间为
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825004556663857.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825004556678928.png)
由
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825004556694489.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825004556585752.png)
⑶
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/201408250045567411333.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/201408250045567561356.png)
当H-h+x=h-x,即x=h-H/2时,小球运动时间最长
x=h-H/2,符合(2)的条件
代入得:
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825004556600754.png)
![](http://thumb2018.1010pic.com/images/loading.gif)
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