A child places a spring of negligible mass between two toy cars of masses 112 g and 154 g. She compresses the spring and ties the cars together with a piece of string. When she cuts the string, the spring is released and the cars move in opposite directions. The 112 g car has a speed of 1.38 m/s. What is the speed of the second car? If the spring had been compressed 4 cm, then what is the force constant of the spring?