Max induction of spring with two colliding trains

Question

Two trains collide, train A weights 15.000 kg and moves with 10km/u (2.77... m/s) to the right, the other train weights 30.000kg and moves with 20km/u (5.55m/s) to the left. Train A has a spring on its right side with k=3MN/m. What is the max induction of that spring?

I know it has something to do with T1 +V1 = T2 V2, but I'm confused because the spring is moving too.
 

Comments

This is not graduate-level, voting to close. 500 rep users please upvote the closevote here.

Answer 1

Found it myself, First I had to look what the result of the two trains collision would be. (ma*va1+mb*vb1 = (ma+mb)*v2) and then I could fill in the T1 + V1 = T2 + V2 formula with T1 = 1/2*ma*va² + 1/2*mb*vb² and V1 = 0 since s1 of the spring is. And T2 = 1/2*(ma+mb)v2² and V2=1/2*k*smax².
Resulting in smax = 0.4809 meters.