Physics
posted by Anya .
the question is to write down a relationship for the potential energy of a body of mass m, when it is a distance r from the center of mass M and radius R.explain all symbols used
and show that if a body is to escape the gravitational influence of the planet, it must be launched from the surface of the planet with a minimum speed, v = (8 pi GR^2 p/3) ^1/2 ..where G is grav. const, and p is the density of the planet

PE= GMm/r ....see the law of gravitation.
1/2 mv^2=GMm/r
remember that density=M/(4/3 PI r^3)