题目

质点所受的力F随时间变化的规律如图所示，力的方向始终在一直线上，已知t=0时质点的速度为零，在图示的t1、t2、t3和t4各时刻中（                                                                                               ）                                                                                                   　   A． t1时刻质点速度最大                B． t2时刻质点速度最大 　   C． t3时刻质点离出发点最远         D．    t4时刻质点回到出发点                                                                                                                                  答案：B

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