A sonar echo returns to a submarine 1.20 s after being emitted. What is the distance to the object creating the echo? (Assume that the submarine is in the ocean, not in fresh water.)

Video Transcript

This is College Physics Answers with Shaun Dychko. A submarine in the ocean which consists of salt water which is important because salt water has a different speed of sound than in freshwater. This submarine emits a sonar sound wave which bounces off some object and that reflection is detected 1.20 seconds after the original emission of the sound. So the sound travels this distance from the submarine to the object which we label L; it travels at distance L twice so the total distance traveled by the sound is 2 times L and you could also say the distance is the speed of the sound multiplied by the time it took to do the entire trip and we'll replace d with 2L and then we can solve for L by dividing both sides by 2. So the distance between the submarine and the object is the speed of sound in salt water multiplied by the time divided by 2. And we look at table [17.1] to find that the speed of sound in seawater is 1540 meters per second and so we multiply that by 1.20 seconds divide by 2 and we get 924 meters is the distance from the submarine to the object.