15. Cart A (mA = 850 g) has a velocity of 4 m/s [right] and is moving along a frictionless surface towards cart B (mB = 450 g), which is moving at 1.0 m/s [left]. Attached to cart B is a long spring, oriented horizontally, as shown in the diagram below. The spring has a spring constant of 1.2 kN/m. Spring a. What is the amount by which the spring is compressed when the separation of the carts is at a minimum? [5 marks] b. What is the speed of each cart after the collision? [5 marks]