1. The problem statement, all variables and given/known data Superman must stop a 120-kmh train 150m to keep it from hitting a stalled car on the tracks. If the train's mass is 3.6 x 10^5 kg, how much force must he exert? Compare to the weight of the train (give as %). How much force does the train exert on Superman?" 2. Relevant equations We just started this unit but I am not entirely sure which equation to use. I know I must find the amount of time it takes to stop, the deceleration of the train, and the forces from the problem. 3. The attempt at a solution So far I've found the time, 9 seconds, and the deceleration, -3.703 (would it be negative?) I need help from this point on and I know it's relevant to Newton's third law of motion. Any help is greatly appreciated.