The speed of sound in water is 1500 meters per second. How far away from an under-sea rock should a deep-sea diver be so that he can hear his own echo?

As given, the speed of the sound $v=1500\ m$

Let $d$ be the distance between the rock and the diver.

To hear his own echo, the time should not be longer than $0.1\ s$.

So, time $t=0.1\ s$

We know that $distance=speed\times time$

So, $2d=v\times t$  [here we take distance $=2d$, as the sound travels twice for echo]

Or $2d=1500\ m/s\times0.1\ s$

Or $d=\frac{150}{2}$

Or $d=75\ m$

Thus, the diver should be $75\ m$ far from the under sea-rock to hear his echo.

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Updated on: 10-Oct-2022

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