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Homework Help: Sound Problem: Find Distance!

  1. Feb 5, 2008 #1
    problem How and which equation?? Please help me!
    At a height of 10 meters above the surface of a lake, a sound pulse is generated. The echo from the bottom of the lake returns to the point of origin 0.140 s later. The air and water temperatures are 20°C. How deep is the lake?

    wavelength = 4(L + 0.4d)
    Vsound = 331.5m/s + .6T

    ok heres what I got from a friend and I know its right but...
    Speed in air: 343 m/s Speed in water: 1482 m/s

    Time in air = 20/343 = 0.058 s
    Time in water = 0.140 - 0.058 = 0.082 s
    Time to hit bottom: 0.082 / 2 = 0.041 s
    d = 1482 (0.041) = 60.8 m

    ...where did the 20 come from on "Time in Air"? is it 10 x 2?
    Last edited: Feb 5, 2008
  2. jcsd
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