1. The problem statement, all variables and given/known data Block A with mass 13kg is moving right on a frictionless table. Block B with mass 1kg is moving left. Block B has a spring on its left side, the side that will hit Block A. THe question is: Which is the same for both after the collision? 1. speed 2. velocity 3. acceleration 4. KE 5. magnitude of momentum 2. Relevant equations Conservation of momentum Conservation of energy 3. The attempt at a solution I eliminated choices 1-3, but I don't know if you use the conservation of momentum or the conservation of energy for this problem. I know that the collision has to be elastic to use CoE but I know you can always use conservation of momentum. So, which one is the right answer?