Amass of 1 slug is attached to a spring whose constant is 5 lb/ft. initially, the mass is released 1 foot below the equilibrium position with a downward velocity of 11 ft/s, and the subsequent motion takes place in a medium that offers a damping force that is numerically equal to 2 times the instantaneous velocity. (a) find the equation of motion if the mass is driven by an external force equal to f(t) = 24 cos 2t + 6 sin 2t.