A subway train has three cars, each weighing 1.20 x 105 N. The frictional force on each car is 103 N, and the first car, acting as an engine, exerts a horizontal force of 4.80 x 104 N on the rails. (a) What is the acceleration of the train? (b) What is the tension in the coupling between the first and second cars? (c) What is the tension between the second and third cars?