题目内容
如图所示,A是一质量为M的盒子,B的质量为
,A、B用细绳相连,跨过光滑的定滑轮,A置于倾角θ=30°的斜面上,B悬于斜面之外而处于静止状态.现在向A中缓慢加入沙子,整个系统始终保持静止,则在加入沙子的过程中( )
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/201408250006171755829.png)
A.绳子拉力逐渐减小
B.A对斜面的压力逐渐增大
C.A所受的摩擦力逐渐增大
D.A所受的合力不变
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825000617144520.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/201408250006171755829.png)
A.绳子拉力逐渐减小
B.A对斜面的压力逐渐增大
C.A所受的摩擦力逐渐增大
D.A所受的合力不变
BCD
试题分析:以A和沙子整体做为研究对象,初始未加入沙子前,由图可知,
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/201408250006171911010.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825000617206384.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/201408250006172221183.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/201408250006172371217.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825000617269465.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825000617269304.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825000617284411.png)
![](http://thumb2018.1010pic.com/images/loading.gif)
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