A car of mass 1000kg traveling north at 4m/s collided with a car of mass 500kg traveling east at 6m/s. The two cars stick together. What is the magnitude of momentum of the two car system immediately after the collision

Why does the equilibrium position of the spring change when a mass is added to the spring? will the mass oscillate around the new equilibrium position of the spring or the previous position without a mass attached to the spring? if the equilibrium position of the spring changes by 20 cm (assuming no initial mass) when a mass is added to the spring with constant 4.9 kg/s^2, what is the mass of the object attached to the spring?