A 2-kg mass is attached to a spring hanging from the ceiling, thereby causing the spring to stretch 20 cm upon coming to rest at equilibrium. At time t 0, the mass is displaced 5 cm below the equilibrium position and released. At this same instant, an exter- nal force 0.3 cos t N is applied to the system. If the damping constant for the system is 5 N-sec/m, determine the equation of motion for the mass. What is the resonance frequency for the system