A 2.5-kg cart is rolling along a frictionless, horizontaltrack towards a 1.5-kg cart that is held initially at rest. Thecarts are loaded with strong magnets that cause them to attract oneanother. Thus, the speed of each cart increases. At a certaininstant before the carts collide, the first cart's velocity is +4.5m/s, and the second cart's velocity is -2.5m/s.
(a) What is the total momentum of the system of the two carts at this instant?
(b) What was the velocity of the first cart when the second cart was still at rest?