1. The problem statement, all variables and given/known data The proper average lifetime of pi mesons is 2.6*10^-8 s. If a beam of these pi mesons is moving with a speed of 0.9c, then with respect to rest frame of the pi meson, how far does it travel before it decays? 2. Relevant equations L=L_0 sqrt(1-(v/c)^2) T=T_0 sqrt(1-(v/c)^2) 3. The attempt at a solution I thought it was 0 because it's not moving with respect to itself. My teacher says this is a trick question... so I was wondering if zero is not the case even though it seemed at first simple enough.