v前4s平均=(2.4m/s+2m/s)/2=2.2m/s
v第4s平均=(2.4m/s+2.3m/s)/2=2.35m/s
x第4s内=((2.4m/s0²-(2.3m/s)²)/(2*0.1m/s²)=2.35m