What is the tension in the coupling

[8parks11]

An inter city Express locomotive pulls 14 cars, each with a mass of 53,000 kg. What is the tension in the coupling between the thrid and fourth cars when the acceleration of the train is 0.26m/s.


ok so I am looking for T.
F=ma
53000(0.26) = T?
i don't think this is correct because they mentioned 3,4 cars
or was that just random?


I don't know at all.




Added:
a) What is the minimum time in which one can hoist a 1.00-kg rock height of 10.0m if the string used to pull the rock up has a breaking strength of 10.8 N? Assume the rock to be initially at rest.
b) If the string is replaced by one that is 50% stronger, by what percentage will the minimum time for the hoist be reduced.


alright a) i just used a= 2(x-xo)/t^2 and then i got 2(10)/t^2 = 10.8/1
so i got 10.8=20/t^2 and so t would be root 10.8 but the answer is 4.5s... why??

b) i need to get a) to solve this...

 

[Pyrrhus]

Don't you have an idea about the whole system?

Your whole system is 14 cars, being pulled by a train with an acceleration of 0.26 m/s^2. Think about the problem of the 3 blocks (between each block there's a string) being pulled by a force F.

 

[8parks11]

so there is T1 T2 and T3 and i have to find T3.
isnt T3
F=ma
F= (m1+m2+m3).26
so it would be 3(53000)(0.26) = T?