A projectile is launched from Earth’s surface and reaches a maximum height of h. Assume that h << RE, where RE is the radius of the Earth.
Show that the variation in gravitational potential energy of Earth with height can be written as U=mgz(1-z/r), where g=GM/R^2and z is the height of an object above the Earth’s surface. Hint, recall that you can set the zero-point of the potential energy to any convenient value.