A 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 and (b) the acceleration of the train.

Force exerted by the engine F = 40000N

frictional force f = 5000N

(a) Applying Newton's second law on the system, 

∑F_{net ​}= ma

From figure,   [Fig. 1]

F_net​ = F− f

     =40000−5000

     =35000 N

Hence the net accelerating force is 35000 N

(b) According to Newton's 2nd law, we can write:

But F_net ​= (Total mass) × (Acceleration)  [Fig 2]

35000 = (M+5m).a

where 5m is the mass of the 5 wagons attached to the train  and M is the mass of the train.

mass of each wagon is 2000 kg that is  m=2000kg.

a = 35000 ​/ (M+5m)

a = 35000 N​ / (8000kg+(5×2000kg))=1.944 m/s²

Therefore the acceleration of the train is 1.944 m/s²