An echo-sounder in a trawler (fishing boat) receives an echo from a shoal of fish $0.4\ s$ after it was sent. If the speed of sound in water is $1500\ m/s$, how deep is the shoal?
(a) $150\ m$
(b) $300\ m$
(c) $600\ m$
(d) $7500\ m$

Here speed of the sound i  water $v=1500\ m/s$

Time taken by sound to reach and return $t=0.4\ s$

So, the time taken to reach $=\frac{t}{2}\ s$

$=\frac{0.4}{2}\ s$

$=0.2\ s$

Therefore, distance$=speed\times time$

$=1500\ m/s\times 0.2\ s$

$=300\ m$

So the depth of the shoal is $300\ m$

So, option (b) is correct.

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Updated on: 10-Oct-2022

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