Question

Question 7 NCERT Pg 128

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;

(b) the acceleration of the train; and

(c) the force of wagon 1 on wagon 2

{The explanation of this question on the Byju's premium app is wrong; the weight of the engine has not been considered}

Answer 1

Given, force of engine = 40000 N
Force of friction = 5000 N
Mass of engine = 8000 kg
Total weight of wagons = 5 x 2000 kg = 10000 kg
(a) The net accelerating force
= Force exerted by engine – Force of fricition
= 40000 N – 5000 N = 35000 N
(b) The acceleration of the train
We know that, F = mass x acceleration
Or, 35000 N = (mass of engine + mass of 5 wagons) X a
Or, 35000 N = (8000 kg + 10000 kg) X a
Or, 35000N = 18000 kg X a
⇒a=35000N/18000 kg=
1.944m/s^2
(c) The force of wagon 1 on wagon 2 = mass of four wagons x acceleration
⇒F=4×2000 kg×1.944ms−2⇒F=4×2000 kg×1.944ms-2
⇒F=8000 kg×1.944ms−2⇒F=8000 kg×1.944ms-2
⇒F=1552N⇒F=1552N
Thus, (a) The net accelerating force = 35000N
(b) The acceleration of train = 1.944 ms–2
(c) The force of wagon 1 on 2 = 1552 N