The roller coaster is traveling at 40 ft/s when it reaches its lowest point A. Determine the normal force which it exerts on the tracks at this...

The roller coaster is traveling at 40 ft/s when it reaches its lowest point A. Determine the normal force which it exerts on the tracks at this instant and the rate of increase in its speed. Assume the car is free to roll and its total weight, including the passenger, is 800 lb. Neglect the mass of the wheels and the size of the car.