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  1. Class 9
  2. Chapter 12 Class 9 - Sound

Transcript

Question 1 Page 168 An echo is heard in 3 s. What is the distance of the reflecting surface from the source, given that the speed of sound is 342 m s–1? Speed of sound = v = 342 m/s Time taken for hearing the echo = t = 3 s Let the total distance travelled by the sound = 2d Distance of the reflecting surface from the source = Total distance / 2 = 2d/2 = d Now, Speed of sound = (𝐷𝑖𝑠𝑡𝑎𝑛𝑐𝑒 𝑡𝑟𝑎𝑣𝑒𝑙𝑙𝑒𝑑 𝑏𝑦 𝑠𝑜𝑢𝑛𝑑)/(𝑇𝑖𝑚𝑒 𝑇𝑎𝑘𝑒𝑛) v = 2𝑑/𝑡 v × t = 2d 2d = v × t d = (𝑣 × 𝑡)/2 d = (342 × 3)/2 d = 171 × 3 d = 513 m Distance between reflecting surface and source is 513 m

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CA Maninder Singh
CA Maninder Singh is a Chartered Accountant for the past 9 years and a teacher from the past 16 years. He teaches Spoken English, Written English, Grammar and Vocabulary at Englishtan.