This is another problem from the same homework set that I was working on earlier. Again I believe conservation of momentum is the key formula. 1. The problem statement, all variables and given/known data An 8000kg freight car rests against a spring bumper at the end of a railroad track. The spring has constant k=3.2*10^5. The car is hit by a second car of 7600kg mass moving at 6.8 m/s, and the two cars couple together. 1.) What is the maximum compression of the spring? and 2.) What is the speed of the two cars together when they rebound from the spring? 2. Relevant equations M1V1+M2V2=(M1+M2)Vfinal F=-kx. 3. The attempt at a solution I am having trouble bringing the compression of the spring into the equation. In order to find the compression I need the Force that the collision of the cars exert on it using F=m*a. I can kind the mass easily it the combination of both of the cars or 8000kg+7600kg=15600kg. How do I find the acceleration. I know that acceleration is change of velocity over time. I could find the velocity of the coupled cars using the conservation of momentum equation but I still don't have time. This is were I reach my dead end in my logic. A nudge in the right direction would help a ton. Thanks.