1. The problem statement, all variables and given/known data A roller coaster is going down on a track (see image below, the track itself is highlighted in red) without initial velocity. What is the coefficient of friction between the roller coaster and the track? height at which the cart starts (h) = 12m weight of the car (m) = 620kg angle of the track (α) = 40° radius of the circle (r) = 8m normal force acting on the cart in the moment it reaches the lowest point (N) = 22,900N 2. Relevant equations I managed to calculate the energy lost during the process, but I have no idea what to do next. 3. The attempt at a solution I calculated the energy of the cart at the highest and lowest points (hopefully my thought process is visible on the image) and the difference of the two is the energy lost due to friction.