A 2.00 kg cart is rolling across a frictionless, horizontal track toward a 1.50 kg cart that is held initially at rest. The carts are loaded with strong magnets that cause them to attract one another. Thus, the speed of each cart increases. At a certain instant after the carts collide, the first cart's velocity is 4.50 m/s, and the second cart's velocity is 2.20 m/s. What was the velocity of the first cart when the second cart was still at rest