How can you determine if energy was conserve in a momentum problem? Let's say a small mass "m" hits a larger stationary mass "5m" where the smaller mass "m" flies bounces upward and the larger mass "5m" bounces in a negative downward direction. So from them bouncing off each other I know that it's an elastic type of collision. What I also know is that the initial velocity of both masses are not the same after impact. Can any of these clues allow me to tell if energy was conserve within the system? Note: The picture is just something I made up and the values of the different velocities just demonstrate that the smaller ball loses speed after impact. Does that mean that energy is not conserved since the smaller ball losses speed and therefore it losses kinetic energy? Does this make it an elastic collision instead of a perfectly elastic one?