Exploding Spring 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 = 3.5 kg. The carts are pushed toward one another until the spring is compressed a distance 1.2 m. The carts are then released and the spring pushes them apart. After the carts are free of the spring, what are their speeds? Im sorry but I am utterly confused by this problem.. I am pretty sure that I must first use conservation of energy to find momentum then conservation of momentum to find velocity. Exactly how I apply all these concepts together is scrambling my brain.. please help!!