a frictionless rollercoaster car of mass=843 kg tops the first hill with speed v=18m/s ans height=40m. What is the speed…

a frictionless rollercoaster car of mass=843 kg tops the first hill with speed v=18m/s ans height=40m. What is the speed of the car at point b when a is the height as the first hill and b is at h/2?