Tension in coupling between 2nd and 3rd freight cars

[chrizzilla]

Homework Statement

A locomotive is pulling 15 freight cars, each of which is loaded with roughly the same weight. The mass of each can be taken to be 37,000 kg. If the train is accelerating at 0.72 m/s^2 on a level track, what is the tension in the coupling between the second and third cars? The car nearest the locomotive is counted as the first.

Homework Equations

F=ma

The Attempt at a Solution

I used F=ma to find that 37,000 kg * 0.72 m/s^2 = 26640 N. I know that this is the force for each traincar, I just don't know what to do with it.

 

[chrizzilla]

Nevermind, I figured it out.

Since we are looking at the tension between the second and third cars, we only have to look at the force of 13 cars. You simply have to multiply the weight of one car by 13 and use the equation F=ma to calculate:

F = (13)(37,000kg)(.72m/s^2)

F= 346,320 N