A 6000 kg freight car rolls along rails with negligible friction. The car is brought to a rest by a combination of two coiled springs as illustrated in the Figure. After the first spring compresses a distance of 0.3 m, the second spring comes on and increases the force as shown in the graph. The car is brought to rest after 0.5 m by the two spring system.
(a) Look at the graph. What is the work done on the springs?
(b) What was the initial speed of the car?