A massless spring of spring constant 20 N/m is placed between two carts. Cart 1 has a mass M1 = 5 kg and Cart 2 has a mass M2 = 2 kg. The carts are pushed toward one another until the spring is compressed a distance 1.7 m. The carts are then released and the spring pushes them apart. After the carts are free of the spring, what are their speeds? a) velocity of car 1 =? b) velocity of car 2 =? I know that for this problem, I got to use conservation of momentum and conservation of energy, but I don't even know how to even start off this problem. Major help needed!