1. The problem statement, all variables and given/known data Oh boy... Here we go... At what minimum speed must a roller coaster be traveling when upside down at the top of a circle so that the passengers will not fall out? Assume a radius of curvature of 7.4 m. I honestly have nothing. To begin with, I drew a free-body diagram but got nowhere considering the teacher never explained 'radius of curvature'. I've tried searching on the Internet but all I get are a bunch of formulas in geodesy and aren't applicable to the problem. It's not in the book either (Giancoli PHYSICS Updated Edition 2009). 2. Relevant equations Ac=v^2/R [tex]\SigmaF[/tex]=mv^2/R 3. The attempt at a solution Tried setting up a free-body diagram and got nowhere.