28.某人用10牛的拉力,沿斜面将重为16牛的物体匀速地拉上长为4米

 28.某人用10牛的拉力,沿斜面将重为16牛的物体匀速地拉上长为4米,高为2米的斜面顶端。该斜面的机械效率η及斜面对物体的摩擦力f大小分别为

(A)η=O.5f=8牛;      (B)η=O.5f=2牛;

(B)η=0.8f=8牛;      (D)η=O.8f=2牛。

答案

D

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