A 2.3kg cart is rolling across a frictionless, horizontal track toward a 1.5kg 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 before the carts collide, the first cart's velocity +4.5m/s , and the second cart's velocity is -1.9m/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?