题目内容
(1)物体从A传送到B需要的时间为多少?
(2)物体从A传送到B过程中在传送带上留下的划痕多长?
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241156471023952.gif)
(1)
(2)![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824115647429411.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824115647133493.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824115647429411.gif)
(1)(10分)物体放上传送带以后,开始一段时间滑动摩擦力方向沿传送带向下,其运动加速度 ![](http://thumb.1010pic.com/pic2/upload/papers/20140824/2014082411564744573.gif)
。
当物体的速度达到10m/s时,其对应的时间和位移分别为:
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824115647476624.gif)
<L=16m
由于
<tan37°,此后物块相对传送带继续加速下滑。即物体受到的摩擦力变为沿传送带向上,其加速度大小为:
。
设物体完成剩余的位移
所用的时间为
,则
,即
解得:![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824115647585674.gif)
所以:
。
(2) (5分)前一阶段传送带快,划痕长
,第二阶滑块快,划痕长
。两段划痕重合,故划痕总长
。
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/2014082411564744573.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824115647461956.gif)
当物体的速度达到10m/s时,其对应的时间和位移分别为:
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824115647476624.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824115647492528.gif)
由于
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824115647492290.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824115647507935.gif)
设物体完成剩余的位移
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824115647523200.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824115647539204.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824115647554593.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824115647570708.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824115647585674.gif)
所以:
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824115647133493.gif)
(2) (5分)前一阶段传送带快,划痕长
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824115647617517.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824115647632549.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824115647429411.gif)
![](http://thumb2018.1010pic.com/images/loading.gif)
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