题目内容
如右图,水平轨道上有一楔形物体
,其斜面上有一小物块
,
与平行于斜面的细绳的一端相连,细绳的另一端固定在斜面上.
与
之间光滑,
和
以共同速度在水平直轨道的光滑段向左滑行. 当它们刚运行至轨道的粗糙段时,下列说法中正确的是
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/201408250008422404644.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825000842115283.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825000842130299.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825000842130299.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825000842115283.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825000842130299.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825000842115283.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825000842130299.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/201408250008422404644.png)
A.绳的张力不变 |
B.绳的张力增加 |
C.![]() ![]() |
D.地面对![]() |
C
试题分析:在光滑段运动时,物块a及物块b均处于平衡状态,对a和b整体受力分析,受重力和支持力,二力平衡;对b受力分析,如上图,受重力、支持力、绳子的拉力,
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/201408250008422861669.jpg)
根据共点力平衡条件,有:
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825000842302829.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/201408250008423181027.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825000842333673.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825000842349779.png)
当它们刚运行至轨道的粗糙段时,减速滑行,系统有水平向右的加速度,此时有两种可能;
(一)物块a、b仍相对静止,竖直方向加速度为零,由牛顿第二定律得到:
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/201408250008423181027.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825000842396942.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825000842411896.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825000842427997.png)
(二)物块b相对于a向上滑动,绳的张力显然减小为零,a对b的支持力较之前增大,则b对a的压力较之前增大,对a分析,知地面对a的支持力增大.
综合上述讨论,结论应该为:绳子拉力一定减小;地面对a的支持力可能增加;a对b的支持力一定增加.故C正确,A、B、D错误;故选C.
![](http://thumb2018.1010pic.com/images/loading.gif)
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