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Physics problem echoes

  1. Jan 15, 2017 #1
    The Question:
    A boat is floating at rest in dense fog near a large cliff. The captain sounds a horn at water level and the sound travels through the salt water (1470 m/s) and the air (340 m/s) simultaneously. The echo in the water takes 0.40s to return. How much additional time will it take the echo in the air to return?

    Relevent equations: v=d/t

    My answer:
    d = v∆t

    d = 1470*0.40

    d = 588/2 (I checked online for this question, some ppl got different answers due to this part; 558/2 or just 588?)

    d = 294m

    294/340 = 0.86s

    0.86-0.40 = 0.46

    Additional time = 0.46s
  2. jcsd
  3. Jan 15, 2017 #2

    Doc Al

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    Staff: Mentor

    Realize that the sound must travel to the cliff and back.
  4. Jan 15, 2017 #3


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    Gold Member

    If something takes ##0.4s## to cover a distance and something else takes an extra ##0.46s## to cover the same distance, then the faster thing must be moving approx twice as fast as the slower thing. Is ##1,470m/s## approx twice ##340 m/s##?

    Using this logic can you estimate the answer (approx) in your head?
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