1. The problem statement, all variables and given/known data Consider the reaction A + B -> C + D. Show that this can be an elastic collision if there is no change in the colliding bodies. 2. Relevant equations Law of Conservation of Energy. 3. The attempt at a solution No clue how to approach it, or what exactly they're asking. The solutions manual, which has a fully worked out solution for every other question in the textbook, has this as the solution: "#8. Hmm."