1. The problem statement, all variables and given/known data How far will a beam of muons with kinetic energy (a) 1 MeV, (b) 100 GeV travel in empty space before its intensity is reduced by half? 2. Relevant equations See below 3. The attempt at a solution My main problem with this is that it looks like we won't be taught the relevant material until the day before the work is due in. I could wait, but I'd rather get it sorted beforehand. I'm not asking for the answer, but if someone could give me some kind of relevent equation to get started, I would be very grateful!