1. The problem statement, all variables and given/known data Consider a frictionless roller coaster such as depicted below. The acceleration of gravity is 9.8 m/s2. Passenger cars start at point A with zero initial speed, accelerate as they go down to point B, swing around the circular vertical loop B ! C ! B of radius 30 m, then go on towards further adventures (not shown). When a car goes through the top of the loop (point C), the passengers feel weightless (for just a moment). What is the height hA of the starting point A above the loop’s bottom B? Answer in units of m 2. Relevant equations KE = .5mv^2 PE = mgh 3. The attempt at a solution I know that the system is conservative energy since there is no friction and whatnot, so mgh(a) is the total energy. But what I don't get is, how does weightlessness come into this? If it's weightless, does that mean normal force doesn't exist?