1. a sonar pulse is sent to the ocean bottom which is 25◦ celsius. it takes 4.2 seconds for the wave echo to return to the ship. how deep is the ocean bottom? medium m/s air 0○c 331 air 20○c 343 helium 0○c 972 water 25○c 1,493 seawater 25○c 1,533 copper 25○c 3,560 iron 25○c 5,130

The sonar pulse takes t=4.2 s to reach the ocean bottom and then to travel back tothe ship. If we call d the depth of the ocean bottom, this means that the sonar pulse covered a distance equal to 2d in a time of 4.2 s.

The speed of the sonar pulse is the speed of sound in water at 25C, so looking at the table is v=1493 m/s. Using the relationship between space and time for a uniform motion, and keeping in mind that the total distance covered by the pulse is 2d, we can write:

which becomes

so, the ocean bottom is 3135 m deep.