Question

A dolphin in 25℃ sea water emits a sound directed towards the bottom of the ocean 150m below. How much time passes before it hears an echo?
(Take speed of sound in seawater at 25℃ = 1530 m/s)

Answer 1

Hint: The time taken will be the total distance traveled by the sound divided by the speed of sound. To calculate the time taken for the echo, we need to first calculate the total distance travel by the sound.

Complete step by step answer:
In this question we have a dolphin in 25℃ sea water, and it emits a sound directed towards the bottom of the ocean. We must find out the time taken by the sound to get reflected from the bottom surface of the ocean and then reach back to the dolphin.
To calculate the time taken for the echo, we need to first calculate the total distance traveled by the sound, i.e. from dolphin to the bottom surface of the ocean and then back to the dolphin. It is mentioned in the question that the distance between the dolphin and the bottom surface is 150m. Therefore, the total distance traveled by the sound in water is twice this distance i.e. 300m.
Now that we have calculated the total distance traveled by the sound inside the water, we need to calculate the time taken by the sound to travel that distance. We know that speed is equal to distance traveled divided by time taken. Therefore, time taken will be distance travel divided by the speed.
The speed of sound in seawater at 25℃ is given as 1530 m/s. Therefore, the time taken will be
$time = \dfrac{{distance}}{{speed}} = \dfrac{{300}}{{1530}} = 0.2\sec $