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Sound Waves - Dropping a coin down a well

  1. Sep 12, 2015 #1
    The question is:

    You drop a coin down a well. After 3.2 seconds you hear the sound of the coin splashing into the water surface below. How far below lies the water surface in the well?

    After doing all the work the answer comes out to d = 46.0 m. However, when solving for "d" I had to solve a quadratic so I got two answers (two roots). The first was 46.0, but the other was 25,120 m. Obviously using common sense you can pick out that the correct answer was 46, but just out of curiosity what is the significance of the second answer?
  2. jcsd
  3. Sep 12, 2015 #2


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    2017 Award

    Staff: Mentor

    The other solution should be negative.

    If you let a coin drop from above (using the second, negative solution), the coin arrives 3.2 seconds before a sound emitted at the same time and place (neglecting air resistance). Not what you want here, but still 3.2 seconds difference.
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