A goods train has `25` compartments. Will the tension in coupling between the fourth and fifth compartment be the same as that in the coupling between the 21st and the 22nd compartments ?

Explanation

No .let `P` be the pull of the engine .Considering the first four compartments

`P -4f -T = 4ma`
where f = frictional force no each comparment ,m = mass of each comparment , a =acceleration of the train , T = tension

Considering the free body diagrams of the `21^(st)` comparment
`P - 21 f - T' = 21 ma`
Hence `T + P - 4(f + ma)`
and T' = P - 21 (f + ma)`
`:. T' lt T `