Amass of 1 slug, when attached to a spring, stretches it 2 feet and then comes to rest in the equilibrium position. starting at t = 0, an external force equal to f(t) = 6 sin 4t is applied to the system. find the equation of motion if the surrounding medium offers a damping force that is numerically equal to 8 times the instantaneous velocity. (use g = 32 ft/s2 for the acceleration due to gravity.)