x1=AB=0.015m，x5=EF=0.031m，T=0.1s根据：xm-xn=(m-n)aT²x5-x1=4aT²a=(x5-x1)4T²=(0.031-0.015)/4×0.1²=0.4m/s²BC-AB=aT²BC=aT²+AB=0.4×0.1²+0.015=0.019mvB=(AB+BC)/2T=(0.015+0.019)/0.2=0.17m/s
