1. The problem statement, all variables and given/known data A 40-tonne boxcar A is moving with a velocity of 7.2 km/h when it strikes, and is automatically coupled with, a 12-tonne flatcar B which carries a 20-tonne trailer truck C. Both the flat car and trailer truck are at rest with their brakes released. What is the velocity of the boxcar immediately after the end of the flatcar hits the trailer truck? Neglect friction and assume the impact of the flatcar and trailer truck to be perfectly plastic (e = 0). 2. Relevant equations Conservation of linear momentum. 3. The attempt at a solution Able to calculate the velocity of the coupled pair immediately after impact using conservation of linear momentum. So velocity will be constant until the trailer truck hits the end of the flatcar at which point the velocity of the boxcar changes. Unsure where to go from this point!