Answer:
4 seconds
Explanation:
There are links between cars, they are in between
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.
Here 1 represents the first car which is firmly attached to the engine. So, there are 16 links and each link has a slack of 9 m.
So, total slack
9×16 = 144 cm
Speed of train = 36 cm/s
Time taken by the pulse to travel the length of train is 4 seconds.