Thanks for the help. Please keep thinking about this problem.
The formula doesn't take time into account. The heavier car starts more slowly because it has a greater mass, more inertia. So over the beginning part of the track, the heavier car is slower. Maybe over time it evens out but...
For my science fair project, I am testing the effect of changes in mass on the time it takes a car to complete a roller coaster track. The track is made of hotwheels track and has an initial ramp, two turns and a loop. I used the same car both times (once without added weight and once with an...