Question

A ship sends a pulse of ultrasound and receives an echo 0•3 seconds later. If the speed of sound in water is 1500 m/s calculate its depth.

Answer 1

use direct formulae and you get 500m

Answer 2

We can solve this by using equation,
$speed = \frac{distance}{time}$
Since, the echo is received, means the distance doubled. So,
$speed = \frac{2 \times distance}{time}$
$1500 = \frac{2 \times d}{0.3}$
$1500 \times 0.3 = 2d$
$\frac{450}{2 } = d$
$225ms ^{ - 2}$
I hope this will help you a lot.