题干

如图所示,斜面长10 m,高4 m,用沿斜面方向的推力F,将一个质量为50 kg的货物由斜面底端匀速推到顶端,运动过程中克服摩擦力做功500 J(g取10 N/kg),下列说法正确的是(   )

A:机械效率为80%

B:F=300 N

C:摩擦力为100 N

D:条件不足无法计算

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A

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