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Page No 172: - Chapter 12 - Sound - Ncert Solutions class 9 - Science
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Question 1:
A submarine emits a sonar pulse, which returns from an underwater cliff in 1.02 s. If the speed of sound in salt water is 1531 m/s, how far away is the cliff?
Answer:
Time taken by the sonar pulse to return, t = 1.02 s
Speed of sound in salt water, v = 1531 m s−1
Total distance covered by the sonar pulse = Speed of sound × Time taken
Total distance covered by the sonar pulse 
…..(i)
Let d be the distance of the cliff from the submarine.
Total distance covered by the sonar pulse = 2d
⇒2d=1561.62 [From (i)]⇒d=780.81 m
