如图所示，在倾角为30°、静止的光滑斜面上，一辆在外力作用下加速下滑的小车上悬吊单摆的摆线总处于水平位置。已知车的质量和摆球的质量均为m，下列正确的是（ ）
A．小车加速度为g/2
B．摆线中张力大小一定为
mg
C．小车加速度为2g
D．摆线中张力大小一定 为2mg
答案：C
题目分析：
据题意，先把摆球隔离进行受力分析，如上图，在重力G和拉力T的作用下摆球沿斜面向下加速，其加速度为a=F/m=g/sin30°=2g，而摆球的运动情况和整体的运动情况一致，所以整体的加速度也为2g，则A选项错误而C选项正确；摆线的张力T=mgtan60°=
mg，所以B、D选项错误。
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