1. The problem statement, all variables and given/known data An unstable particle called the pion has a mean lifetime of 25ns in its own rest frame. A beam of of pions travels through the lab with a speed of 0.60c. a) what is the mean lifetime of the pions as measured in the lab frame? b) how far does a pion travel ( as measured by lab observers) during this time? 2. Relevant equations I was able to find part a but not sure about part b. the answer our professor porvided was 5.6m what exactly is c? is it unit less? 3. The attempt at a solution I found a using t= 1/γ x t inital for finding how far the pion traveled i was using d=v t with 0.60 for v and 31ns for t. however the units are not correct and my answer is not very clse to the given answer. Thanks in advance :) this gave me an answer of 31 ns.