1. The problem statement, all variables and given/known data A railway engine of mass 100 tonnes is attached to a line of trucks of total mass 80 tonnes. Assuming there is no resistance to motion, find the tension in the coupling between the engine and the leading truck when the train: (a) has an acceleration of 0.020 ms-2, (b) is moving at constant velocity. Answers: (a) 1.6 kN, (b) zero 2. Relevant equations F = ma Weight = mg 3. The attempt at a solution (a) Ftotal = (100+80)*103 * 0.02 = 3600 N Fengine = 100*103 * 0.02 = 2000 N T = 3600 - 2000 = 1600 N (b) Constant velocity = 0 acceleration. But I don't quite understand why there is 0 tension. Any tips? Thank you.