# How long will it take for the echo to return

## Homework Statement

A submarine sends out a sonar wave that has
a frequency of 545 Hz. If the wavelength of the
sound is 2.60 m, how long does it take for the
echo to return when the sound is reflected from
a submarine that is 5.50 km away?

## The Attempt at a Solution

i used the equation p=1/f and i plugged in frequency and got 0.00183 seconds, the right answer should be around 7-8 seconds

SteamKing
Staff Emeritus
Homework Helper

## Homework Statement

A submarine sends out a sonar wave that has
a frequency of 545 Hz. If the wavelength of the
sound is 2.60 m, how long does it take for the
echo to return when the sound is reflected from
a submarine that is 5.50 km away?

## The Attempt at a Solution

i used the equation p=1/f and i plugged in frequency and got 0.00183 seconds, the right answer should be around 7-8 seconds

Well let's see here. Is it perhaps you calculated the period of one wavelength and overlooked the fact that it takes more than one wave of length 2.60 m to cover the distance of 5.50 km to the object and then 5.50 km back again to the sub?

Well let's see here. Is it perhaps you calculated the period of one wavelength and overlooked the fact that it takes more than one wave of length 2.60 m to cover the distance of 5.50 km to the object and then 5.50 km back again to the sub?
thank you so much, i finally got the right answer!