$2.$ A mass$-$spring$-$damper vibrating system with a mass of $18$ kg$,$ a stiffness of $2,800$ N$/$m and a damping coefficient of $48$ N$-$s$/$m is excited by a harmonic force with an amplitude of $280$ N and a frequency of $3\mathrm{.}8$ Hz$.$ Determine the response that represents the motion of the mass if a displacement and an initial velocity of $18$ mm and $2\mathrm{.}8$ m$/$s$,$ respectively, are applied to it$.$