# Potential Elastic Energy between two carts [closed]

I have a problem in which two carts are attached by a compressed spring. I have found that cart $A$ moves at $1.1~\mathrm{m/s}$ to the right and has a mass of $0.39 ~\textrm{kg}.$ Cart $B$ has a mass of $0.18~\textrm{kg}$ and moves at $2.382~\mathrm{m/s}$ in the opposite direction. How do I use the equation $U = kx^2$ to find what the potential elastic energy is?

It isn't making sense to me because I don't know what the displacement of each cart is.

## closed as off-topic by ACuriousMind♦, user36790, Martin, Kyle Kanos, GertFeb 17 '16 at 22:05

This question appears to be off-topic. The users who voted to close gave this specific reason:

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Note that the elastic potential energy stored in a spring is $\frac 1 2 k x^2$.