1. The problem statement, all variables and given/known data We had an air track and let a cart of mass m travel downhill. The we calculated the velocity and firther the kinetic energy K and the gravitational energy U. We did this to show that the total energy in the system stays constant. Now I need to answer the question if I could still show that the total energy would be conserved if the mass was unknown. 2. Relevant equations K=1/2mv^2 U=mgh 3. The attempt at a solution I was looking at the parts where the mass would be involved. This seems to be in both formulas. Thus, my guess is that the mass would be cancel out and it would not matter if I know the mass or not. I could write initial kinetic energy + initial potential energy = final kinetic energy + final potential energy. My problem is that I do not know if I am thinking in the right direction. So, if someone could help me and let me know if I am right or wrong with my thought, that would be great. Thanks.