A pilot makes an outside vertical loop (in which the center of the loop is beneath himof radius 3200 m. At the top of his loop he is pushing down on his seat with only one-half of his normal weight. How fast is he going?"

Newton's law of universal gravitation: Every particle in the universe attracts every other particle with a force that is proportional to the product of their masses and inversely proportional to the square of the distances between them. This force acts along the line joining the two particles.