Answer
$s=\displaystyle \frac{t^{3}}{3}+t+1$
Work Step by Step
The given information is that $s(0)=1$
$s(t)=\displaystyle \frac{t^{3}}{3}+t+C\qquad $ insert the given data to find $C$
$1=0+0+C$
$C=1$
Thus,
$s=\displaystyle \frac{t^{3}}{3}+t+1$