A spring is stretched 0.5 meters by a force of 4 newtons. An object whose mass is 2 kg is attached to this spring, and the system is placed in a medium where the object is subjected to a damping force that is equal to the instantaneous velocity of the object. The object is moved to a position that is 1 meter below the equilibrium point and an initial velocity of 5 m/s in the downward direction is applied. Find the equation of motion for the system.