A glass marble is dropped down an elevator shaft and hits a thick glass plate on top of an elevatior that is descending at a speed of 2.0 m/s. The marble hits the glass plate 3.0 m below the point from which it was dropped. If the collision is elastic how high will the marble rise, relative to the point from which it was dropped? So far, I let the point of impact have potential energy = 0, which would make the top of the fall have a PE of 29.4m J. That would mean that the kinetic energy just before impact would be 29.4m = 0.5mv^2. Solving for v I got 7.7 m/s. All I need help with is figuring out the velocity just after impact, and I think I can take it from there. I thought it was just (7.7 - 2)m/s, but I'm not sure.