Amass weighing 16 lb stretches a spring 3 in. the mass is attached to a viscous damper with a damping constant of 2 lb · s/ft. if the mass is set in motion from its equilibrium position with a downward velocity of 3 in/s, find its position u at any time t. (use g = 32 ft/s2 for the acceleration due to gravity. let u(t), measured positive downward, denote the displacement in feet of the mass from its equilibrium position at time t seconds.)