Using the uncertainty principle for energy and time, estimate the range of the Strong interaction if it is due to the exchange of a pion with rest mass 140GeV (Take the value of h as 4.14x10^-21MeV s) Now I know that Delta T x Delta E is > or = to hbar and that I want DeltaX as a solution. But after having worked out DeltaT using basic algebra it's hard to know where to go. Should I head with E = 1/2 mv^2 to get the velocity then use speed x time to get distance? If so how do I find the mass of a pion? Or I could try and get the momentum but encounter similar problems. If there's a simple way using the wave function then I might not know it as I really wasn't sure about that lecture and am working on finding out more. Any help appreciated, thanks.