1. The problem statement, all variables and given/known data A car in an amusement park ride rolls without friction around the track shown in the figure http://session.masteringphysics.com/problemAsset/1041727/8/YF-07-32.jpg It starts from rest at point A at a height h above the bottom of the loop. Treat the car as a particle. What is the minimum value of h (in terms of R) such that the car moves around the loop without falling off at the top (point B)? 2. Relevant equations Ugrav1 + K1 = Ugrav2 + K2 circumference of a circle = 2*pi*R 3. The attempt at a solution I thought that since there is no friction, energy is conserved so the energy used to roll up and down the loop is the energy transformed from gravitational potential energy to kinetic energy. So, I thought the height should be 2*pi*R to make it around the loop, but it is wrong. So, how can I decide what the minimum value of h should be?