8000 kg engine pulls a train of 5 wagons, each of 2000 kg, along a horizontal track. If the engine exerts a force of 40000 N and the track offers a friction force of 5000 N, then calculate:
(a) The net accelerating force,
(b) The acceleration of the train, and
(c) The force of wagon 1 on wagon 2
(a) Given,
Force of engine = 40,000 N
Force of friction = 5,000 N
So,
Net accelerating force, F = Force of engine – Force of friction
= 40000 – 5000
= 35000 N
(b) Net force exerted by the engine = 35000 N
The mass of 1 wagon of train = 2000 kg
The mass of 5 wagons of train = 2000 × 5
= 10000 kg
In other words, the mass of whole train is 10000 kg
We know that,
Net force = mass of train × acceleration
F = m × a
35000 = 10000 × a
a = 
m/s2
a = 3.5 m/s2
Therefore, the acceleration of the train is 3.5 m/s2
(c) There are total 5 wagons behind the engine (which have been marked 1, 2, 3, 4 and 5 in the figure) and there are only 4 wagons behind wagon 1.
Force of wagon 1 = Mass of 4 wagons × Acceleration of train
= 2000 × 4 × 3.5
= 28000 N