On a low-friction track, a \(0.36-\mathrm{kg}\) cart initially moving to the right at \(2.05 \mathrm{~m} / \mathrm{s}\) collides elastically with a \(0.12-\mathrm{kg}\) cart initially moving to the left at \(0.13 \mathrm{~m} / \mathrm{s}\). The \(0.12-\mathrm{kg}\) cart bounces off the \(0.36-\mathrm{kg}\) cart and then compresses a spring attached to the right end of the track.

(a) At the instant of maximum compression of the spring, how much elastic potential energy is stored in the spring?

(b) If the spring then returns all of this energy to the cart, and the two carts again collide, what is the final velocity of each cart?