Question

An object is $11km$ below sea level. A ship sends down a sonar signal to confirm how deep the object is. After how long can it expect to get the echo?
(Take the speed of sound in sea water as $1520m{s}^{-1}$.)

• A. $15.30s$
• B. $14.47s$
• C. $12.20s$
• D. $11.13s$

Answer 1

The correct option is B $14.47s$

The total distance travelled by the sonar signal from the ship to the sea bed and back:
$s=2\times 11km=22,000m$

Speed of sound in water, $v=1520m{s}^{-1}$

Time taken by the sound to travel this distance is:
$t=\frac{s}{v}$
$t=\frac{22000}{1520}=14.473s$

Hence, the echo will reach the ship $14.47s$ after the signal is sent.