在倾角为a的光滑斜面上有两个用轻质弹簧相连的物块A,B.C为一垂直固定在斜面上的挡板.A,B质量均为m,弹簧的劲度系数为k,系统静止在光滑水平面上,先用一从0开始缓慢增大的水平力F作用于斜

在倾角为a的光滑斜面上有两个用轻质弹簧相连的物块A,B.C为一垂直固定在斜面上的挡板.A,B质量均为m,弹簧的劲度系数为k,系统静止在光滑水平面上,先用一从0开始缓慢增大的水平力F作用于斜
在倾角为a的光滑斜面上有两个用轻质弹簧相连的物块A,B.C为一垂直固定在斜面上的挡板.A,B质量均为m,弹簧
的劲度系数为k,系统静止在光滑水平面上,先用一从0开始缓慢增大的水平力F作用于斜面,方向水平向左,（物块A一直没离开斜面,重力加速度为g）,下列正确的是（ ）
A.力F较小时相对于斜面静止,F增加到某一个值,A相对于斜面向上滑行
B.力F从0开始增加时,A相对于斜面向上滑行
C.B离开挡板C时,弹簧伸长量为mgsina/k
D.B离开挡板C时,斜面的加速度大小为gcota
要详解,高考临近,

在倾角为a的光滑斜面上有两个用轻质弹簧相连的物块A,B.C为一垂直固定在斜面上的挡板.A,B质量均为m,弹簧的劲度系数为k,系统静止在光滑水平面上,先用一从0开始缓慢增大的水平力F作用于斜
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