题目内容
(12分)如图所示,有一条沿顺时针方向匀速传送的传送带,恒定速度v=4 m/s,传送带与水平面的夹角θ=37°,现将质量m=1kg的小物块轻放在其底端(小物块可视作质点),与此同时,给小物块沿传送带方向向上的恒力F=10 N,经过一段时间,小物块上到了离地面高为
=2.4 m的平台上。已知物块与传送带之间的动摩擦因数μ=0.5,(g取10 m/s2, sin37°=0.6,cos37°=0.8).
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/201408250023424862974.jpg)
问:(1)物块从传送带底端运动到平台上所用的时间?
(2)若在物块与传送带达到相同速度时,立即撤去恒力F,计算小物块还需经过多少时间离开传送带以及离开时的速度?
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825002342470313.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/201408250023424862974.jpg)
问:(1)物块从传送带底端运动到平台上所用的时间?
(2)若在物块与传送带达到相同速度时,立即撤去恒力F,计算小物块还需经过多少时间离开传送带以及离开时的速度?
1.25s 1s 2m/s
试题分析: (1)对物块受力分析可知,物块先是在恒力作用下沿传送带方向向上做初速为零的匀加速运动,直至速度达到传送带的速度,由牛顿第二定律
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/201408250023425171127.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825002342548660.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825002342564712.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825002342580815.png)
物块达到与传送带同速后,对物块受力分析发现,物块受的摩擦力的方向改向
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/201408250023425951102.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825002342611422.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/201408250023426261008.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825002342642899.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825002342658672.png)
(2)若达到同速后撤力F,对物块受力分析,因为
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825002342673659.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825002342704735.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/201408250023427201046.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825002342736669.png)
设物块还需
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825002342751310.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825002342767319.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825002342798700.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825002342814618.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825002342829624.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825002342845411.png)
![](http://thumb2018.1010pic.com/images/loading.gif)
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