# Homework Help: Echo in the ocean

1. Nov 16, 2006

### mikefitz

A geological survey ship mapping the floor of the ocean sends sound pulses down from the surface and measures the time taken for the echo to return. How deep is the ocean at a point where the echo time (down and back) is 7.07 s? The temperature of the seawater is 25°C. Find the answer in km

7.07 / 2 = 3.535 seconds to get from surface to ocean bedrock.
v = 331 + .6*25 = 346 m/s

3.535 * 346 = 1223.11 m ==> 1 223.11 meters = 1.22311 kilometers

This is wrong according to the online homework I'm doing?

2. Nov 16, 2006

### OlderDan

Perhaps you need the speed of sound in sea water instead of air?

3. Nov 16, 2006

### interested_learner

Your math is correct as far as I can see. However.... the equation you are using for the speed of sound is for air. It is different in water. The actual equation is very complex and dependent on salinity and pressure as well as temperture. You obviously were not given salinity and pressure varies with depth so maybe I am making this too complex. Ideas anyone?

Just for interest: Salinity changes in the oceans causes the sound to bend and reflect in an unpredictable manner. This allows subs to hide beneath various layers making sub hunting a very difficult problem.