1. The problem statement, all variables and given/known data I don't know if anyone can help me with this without having done the lab, but I thought I'd give it a shot. Ok, so I did a lab in my physics class where we used little rollercoasters to find the PE and KE of a marble at various heights and speeds. Here is the question in my lab write-up that has me stumped. How can you use energy conservation to predict the speed of the marble from the height? 2. Relevant equations PEi + KEi = PEf = KEf 3. The attempt at a solution I know that you can obtain the equation Vf = √2ghi from energy conservation, but that doesn't seem to be working when I plug in the height. It isn't coming out to the correct speed which I already calculated.