8. (8 points) (i) (6 pts) Consider a roller coaster (mass = 300 kg) that moves along the track shown. Assume all friction is negligible and ignore the kinetic energy of the roller coaster's wheels. Assume the roller coaster starts with a speed of 20 m/s at point A. The heights are h, = 36 m and h = 18m. Set the zero for gravitational potential energy to be at altitude C. a) What is the mechanical energy at the top of the hill? b) What is speed at point B? c) Find the speed of the roller coaster at point C