Let and denote the speeds of the first and the second blocks, respectively, after the collision. We are given that and we would like to find . In elastic collisions, kinetic energy is conserved. The initial kinetic energy is
The final kinetic energy is Setting the initial kinetic energy equal to the final kinetic energy gives Dividing both sides by simplies this equation to Solving for gives Therefore, answer (C) is correct. |

Please send questions or comments to X@gmail.com where X = physgre.