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如圖,質(zhì)量為m的物體在與水平方向成α角的拉力作用下做勻速直線運(yùn)動,物體與水平面間的動摩擦因數(shù)為μ,則物體所受摩擦力的大小為(                                                    )                                        

                                                                                                      

    A.         Fcosα            B. Fsinα       C.  μmg D. μ(mg﹣Fsinα)

                                                                                                                               

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