A rocket is launched from the surface of a planet and moves along a radial path, as shown in the figure below.
The planet may be considered to be an isolated sphere of radius with all of its mass
concentrated at its centre. Point A is a distance
from the surface of the planet. Point B is a distance
from the surface. Show that the difference in gravitational potential
between points A and B is given by the expression
where is the gravitational constant.