如图所示，位于水平桌面上的物块P，由跨过定滑轮的轻绳与物块相

如图所示，位于水平桌面上的物块P，由跨过定滑轮的轻绳与物块相连，从滑轮到P和到Q的两段绳都是水平的，已知Q与P之间以及桌面之间的动摩擦因数都μ，两物块的质量都是m，滑轮轴上的摩擦不计，若用一水平向右的力F拉P使做匀速运动，则F的大小为

A．4μmg	B．3μmg
C．2μmg	D．μmg

答案

A解析:
略

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如图所示，位于水平桌面上的物块P，由跨过定滑轮的轻绳与物块相

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