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**1. Homework Statement**

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. Homework 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.