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[单选题]
质量为M的人站在地面上，用绳通过定滑轮将质量为m的重物从高处放下，如图所示，若重物以加速度a下降，则人对地面的压力为（ ）
A
(M+m)g-ma
B
M(g-a)-ma
C
(M-m)g+ma
D
Mg-ma
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参考答案
试题答案：
C
答案解释：
参考解析：【答案】C 【考情点拨】本题考查了受力分析的知识点。 【应试指导】对重物受力分析可得绳的张力F=mg-ma，对人受力分析可得人对地面的压力为N=Mg-F，两式联立得N=(M-m)g-ma。
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