1. The problem statement, all variables and given/known data The normal force equals the magnitude of the gravitational force as a roller coaster car crosses the top of a 46m--diameter loop-the-loop. 2. Relevant equations What is the car's speed at the top? 3. The attempt at a solution the answer is in m/s I have several equations but I really don't know what to do with them... the sum of Fr=nr+(Fr)r=n+mg=m(Vtop)^2/r and n=m(Vtop)^2/r-mg Vc=SQRTrmg/m=SQRTrg wc=SQRTg/r I'm really lost on this one.