Particle in 1-D Box: Pressure Force on Wall

[libai]

This seems a simple problem, but managed to confuse me and my friends a bit, it's definitely not a standard problem from the text-books.
Regard a particle of mass m in a 1 dimensional box of length L (which can be seen as a infinitely deep potential well). What is the 'pressure force' on the wall? (please forgive me my vagueness, I translated this question from chinese).
Thanks for your help!

 

[Fredrik]

Calculate the energy levels. (This is pretty standard). Then calculate the pressure as P=-dE/dL. (In 3 dimensions it would be -dE/dV, where V=L³).