1. The problem statement, all variables and given/known data Use the dispersion relation to find the group velocity v_group and phase velocity v_phase. 2. Relevant equations omega(k) = [(hbar)k^2]/2m 3. The attempt at a solution v_group = domega(k)/dk = [hbar]k/m = h/m lambda = p/m = v This isn't right. v_phase = omega / k = 2pi f/(2pi/lambda) = f lamda = v again... is this right?, doesn't look it but as far as I can see there is no mistake in the calc as I have doing it several times already, am I goign wrong in my physics?