Question

NCERT CLASS IX - Science Textbook
Chapter 12 - Sound

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 1

Since, distance = (speed × time) ÷ 2
                         = (1531 × 1.02) ÷ 2
                         = 1561.62 ÷ 2
           distance = 780.81 metres

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Answer 2

According to the Question

Sound = 1531 m/s^-1

Echo return time = 1.02 sec

As per formula we get

2d = vt

$\tt d = \dfrac{vt}{2}$

$\tt d = \dfrac{1531\times 1.02}{2}$

= 780.81m

= 781 m