1. A bullet train has a maximum acceleration of $0.72m{s}^{-2}$.

A particular bullet train leaves a station at time $t=0$ seconds and its displacement, $sm$, from the station is modelled using the equation 

$s=\frac{3}{200}{t}^{3}0\leqt\leq8$

Show that it takes 8 seconds for the bullet train to reach its maximum acceleration.