3at^2=3.6m-2.4m
t=1s,a=0.4m/s^2
根据匀变速直线运动相邻相等时间内位移差相等得at^2=0.4
则第二秒位移2.0m,低一秒位移1.6m,第四秒位移2.8m,第五秒位移3.2m
初速度根据x=vt+(at^2)/2,带入x=1.6m,t=1s,a=0.4m/s^2,解得v=1.4m/s
平均速度=（1.6m+2m+2.4m+2.8m+3.2m+3.6m)/6s=2.6m/s