A railway engine of mass 50 ton is pulling a wagon of mass 40 tons with a force of 4500N. The resistance force acting is 1N per ton. The tension in the coupling between the engine and the wagon is

By using the equation

F = ma

The acceleration of the combined masses are

4500 = (50+40)a

a = 4500/90

The acceleration is 50$\mathrm{m}/{\mathrm{s}}^2$

The tension in the coupling between the engine and wagon is given as

T = 40×50

Hence the tension is 2000N