Chapter 11

NCERT
Class 9
Science
Solutions
1. An echo is heard in 3s. What is the distance of the reflecting surface from the source, given that the speed of sound is 342 ms–1?

Question:

An echo is heard in 3s. What is the distance of the reflecting surface from the source, given that the speed of sound is 342 ms–1?

Answer:

Speed of sound in air = 342 m/s

Time to hear the echo = 3 s

Distance from the source to the reflecting surface,

2d = v x t

d = (v x t) / 2

d = (342 x 3) / 2

d = 513 m

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