A 6000 kg freight car rolls along rails with negligble friction. The car is brought to rest by a combination of 2 coiled springs. Both obey Hooke's law with k1=1600 N/m and k2=3400 N/m. After the first spring compresses a distance of 30 cm, the second springs acts with the first to increase the force as additional compression occurs in the graph. The car comes to rest 50 cm after first contacting the 2 spring system. Find the car's initail speed. I have no idea on how to do this problem.