汽車剎車后,停止轉(zhuǎn)動的輪胎在地面上發(fā)生滑動,可以明顯地看出滑動的痕跡,即常說的剎車線.由剎車線長短可以得知汽車剎車前的速度大小,因此剎車線的長度是分析交通事故的一個(gè)重要依據(jù).若汽車輪胎跟地面的動摩擦因數(shù)是0.6,剎車線長是12m,則可知汽車剎車前的速度大約是(    )                                      

    A.          7m/s               B. 10m/s        C.     12m/s     D. 20m/s

                                                                                                                               

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