1. The problem statement, all variables and given/known data 1-9: Assume the train is 1.0km long as measured by the observer at C' and is moving at 150km/h. What time interval between the arrival of the wave fronts at C' is measured by the observer at C in S? 2. Relevant equations 3. The attempt at a solution The solution from the manual is Δt=t(back)-t(front)= 500/(c-(150/3.6m/s))-500/(c+(150/3.6m/s))=4.6*10^-13 How can it use the distance it travels in S'? It doesn't travel that distance in S.