Well this isn't really a homework problem, just was curious behind the reasoning. In a lab we rolled a marble off the edge of a table, and measured the velocity using: Energy and Free fall trajectory. But when comparing the two there was something like a 60% error, between the two. My Physics teacher doesn't do much, so when I asked him he just shrugged off the question. I think that Free Fall Trajectory is more accurate, but not sure why, its practically a guess.