78. REASONINGNewton’s second law, Equation 4.2a, can be used to find the tension in the coupling between the cars, since the mass and acceleration are known. The tension in the coupling between the 30thand 31stcars is responsible for providing the acceleration for the 20 cars from the 31stto the 50thcar. The tension in the coupling between the 49thand 50thcars is responsible only for pulling one car, the 50th. SOLUTIONa. The tension
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