Dr$.$ John Paul Stapp was U$.$S$.$ Air Force officer who studied the effects of extreme deceleration on the human body. On December $10,1954,$ Stapp rode a rocket sled, accelerating from rest to a top speed of $243\mathrm{.}5$ m$/$s in $5\mathrm{.}81$ s$,$ and was brought jarringly back to rest in only $1\mathrm{.}85$ s$!$ Calculate the magnitude of his acceleration as he was slowing down in in $\text{'}$g$\text{'}$s$,$ where $1$ g $=9\mathrm{.}81$ m$/$s$/$s $($the acceleration due to gravity$).$