A spring is intended to accelerate a projectile of $($mass $1\mathrm{.}02$g$)$ to a velocity of $30$ m$/$s in $0\mathrm{.}10$s$.$ What force is required to retain this spring? What spring constant $($k$)$ would be required of the spring, if the displacement of the spring $($x$)$ was $3\mathrm{.}5$cm$?$