(a) 35000 N (b) 1.944 m/s^{2} (c) 15552 N

**(a) **Force exerted by the engine, *F *= 40000 N

Frictional force offered by the track, *F**f *= 5000 N

Net accelerating force, *F**a *= *F *– *F**f *= 40000 – 5000 = 35000 N

Hence, the net accelerating force is 35000 N.

**(b) **Acceleration of the train = *a *

The engine exerts a force of 40000 N on all the five wagons.

Net accelerating force on the wagons, *F**a *= 35000 N

Mass of the wagons, *m *= Mass of a wagon × Number of wagons

Mass of a wagon = 2000 kg

Number of wagons = 5

∴ *m *= 2000 × 5 = 10000 kg

Total mass (including the mass of engine), M = *m *+ 8000 = 18000 kg

F_{a }= *Ma*

⇒ a = {F_a \over M} = {35000\over18000}

= 1.944 m/s^{2}

**(c) **Mass of 4 wagons (excluding wagon 1) *m *= 2000 × 4 = 8000 kg

Acceleration of the train = 1.944 𝑚/𝑠^{2}

∴ The force of wagon 1 on wagon 2 = 𝑚𝑎 = 8000 × 1.944 = 15552 N.