$($a$)$ What net external force is exerted on a $1100\mathrm{.}0-$kg artillery shell fired from a battleship if the shell is accelerated at $2\mathrm{.}40104$m$/$s$2?2\mathrm{.}40104$m$/$s$2?($b$)$ What is the magnitude of the force exerted on the ship by the artillery shell, and why?