1. The problem statement, all variables and given/known data An object of 2kg moving at 3m/s hits a 4 kg stationary object, causing the stationary object to begin moving at 0.5m/s. How fast is the original object now travelling? It is an elastic collision. 2. Relevant equations Not really sure, 1/2mv^2 I presume. 3. The attempt at a solution None so far, i'm stuck on it and am not sure how to approach it.