1. The problem statement, all variables and given/known data Two long trains carrying coal are traveling in the same direction side by side on separate tracks. One train is moving at 40 ft/sec and the other at 50 ft/sec. In each coal car a man is shoveling coal and pitching it across to the neighboring train. The rate of coal transfer is 4 tons/min for each 100 feet of train length. This rate is the same for both trains. Find the extra force on each train per unit length caused by this mechanism. 2. Relevant equations I think I will need: sum of Forces = Mass * dv/dt but I'm not certain 3. The attempt at a solution I'm not sure exactly what to do. Would you just find the weight of coal added to each train or is there more to it. Does the momentum equation have any use here. I'm confused on how to start this. Any help would be appreciated!