初始时刻为0的话
1)
v(t)=at
s=1/2at^2
v(t)^2=2*a*s
2)
4
3)4m/s,2m/s^2
4)
2s/3
v(t)^2-v(0)^2=2as
v(1)=a
v(2)=2a
4a^2-a^2=2as
a=2s/3