NCERT Solutions for Class 9 Science Chapter 12

Important NCERT Questions

Sound

NCERT Books for Session 2022-2023

CBSE Board and UP Board

Exercises Questions

Page No-174

Questions No-13

# A stone is dropped from the top of a tower 500 m high into a pond of water at the base of the tower. When is the splash heard at the top? Given, g = 10 m s^–2 and speed of sound = 340 m s^–1.

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1. Time for the stone to fall:

Using the formula Distance = 1/2 x g x t² , where g = 10 m/s² and distance is 500 meters:

500 = 1/2 x 10 x t²

This yields t = √((500×2)/10) = 10 s. Thus, the stone takes 10 seconds to reach the water.

2. Time for the sound to travel back up:

The sound must travel twice the tower’s height (up and down) at a speed of 340 m/s:

Distance = 2 x Height = 2 x 500 m = 1000 m

Using Distance = Speed x Time:

Time = (1000 m)/(340 m/s) ≈ 2.94 s

Therefore, adding the time for the stone to fall (10 seconds) to the time for the sound to travel back up (approximately 2.94 seconds), the total time taken for the splash sound to be heard at the top of the tower after the stone is dropped is roughly 10 s + 2.94 s = 12.94 s.