A 20-car train standing on the siding is started in motion by the train’s engine. 2 cm slack is between each of the cars, which are 11 m long. The engine is tightly connected to the first car and moves at a constant speed of 21 cm/s. How much time is required for the pulse to travel the length of the train? Answer in units of s.

1.81 s

Explanation:

From the given information:

The links between the cars are:

1-2, 2-3, 3-4, 4-5, 5-6, 6-7, 7-8, 8-9, 9-10, 10-11, 11-12, 12-13, 13-14, 14-15, 15-16, 16-17, 17-18, 18-19, 19-20.

where;

1 denotes the first car that joins strongly attached to the engine.

There are 19 links from the above connections and each one of them has a 2 cm slack.

Thus; the total slack = 2 × 19 = 38 cm

However, the speed of the train = 21 cm/s

Then, the time taken by the pulse to travel the length of the train is expressed by using the formula:

= length / speed

= 38 / 21

= 1.81 seconds

Thus, the required time = 1.81 s