1. The problem statement, all variables and given/known data A free proton moves back and forth between rigid walls separated by a distance L = 0.01 nm. a) If the proton is represented by a one-dimensional standing de Broglie wave with a node at each wall, show that the allowed values of the de Broglie wavelength are given by λ = 2L/n, where n is a positive integer. b) Derive a general expression for the allowed kinetic energy of the proton and compute the values for n = 1 and 2. 2. Relevant equations K = p2/2m λ = h/p 3. The attempt at a solution The first part seems simple, I could graphically derive that L must equal nλ/L if there are nodes at each end. What I want to make sure about is part b. Would I have to use K = p2/2m, use the mass of a proton, and plug in p = h/λ getting K = h2/2λ2m?