I've been thinking about this for a while now, and I was wanting to know what you guys think. The problem states: Show that a projectile with mass "m" can escape from the surface of a planet if it is launched vertically upward with a kinetic energy greater than MgR, where R is the the planet's radius; ignore air resistance. How do I even start? Its in the chapter deal with "thermal properties of matter; thus the ideal-gas law and van de waals equation". Any ideas?