S=v0t+1/2at2,当t=2时,S=20,当t=-2时,S=12,当t=1时,S=

S=v0t+1/2at2,当t=2时,S=20,当t=-2时,S=12,当t=1时,S=
S=v0t+1/2at2,当t=2时,S=20,当t=-2时,S=12,当t=1时,S=

S=v0t+1/2at2,当t=2时,S=20,当t=-2时,S=12,当t=1时,S=
t=2时:
20=Vo*2+(1/2)a*(2*2)=2Vo+2a
t=-2时:
12=Vo*(-2)+(1/2)a*(-2)*(-2)=-2Vo+2a
联立,解得
a=8m/s^2
Vo=2m/s
t=1时
S=Vo*t+(1/2)at^2=2*1+(1/2)*8*(1*1)=6m