1. The problem statement, all variables and given/known data 1. a) Determine the speed required by a coaster that would cause a rider to experience a normal force of 2mg at the top of a clothoid loop where the radius is 12meters. 2. Relevant equations 3. The attempt at a solution http://i160.photobucket.com/albums/t161/mike_302/physicsq.jpg [Broken] That is my attempt at aa solution. Now, the only problem is that I get a square root negative... Obviously imaginary. Can't do it. But if I made the number positive, I get the right value of 19m/s for speed. Somewhere/somehow, I need to cancel out the negative in there. Can someone explain how? Thanks!