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Homework Help: Finding depth of well

  1. Sep 16, 2015 #1
    1. A rock is dropped into a well of an unknown depth. 20 seconds after the rock is dropped the splash is heard at the top of the well. What is the depth of the well? What is the velocity of the rock when it reached the bottom?

    2. X= Xo + Vo(t) + 0.5(a)(t^2)
    V= Vo + a(t)
    (V^2)= (Vo^2) + 2a(X-Xo)
    Velocity of sound in air=343 m/s
    Acceleration of gravity= -9.80 m/(s^2)

    3. 0= Xo + 0.5(-9.80)(20-t of sound)
    X= 343(t)
    I feel like there isn't enough information, but I'm not sure. Any help would be greatly appreciated.
    Last edited by a moderator: Sep 17, 2015
  2. jcsd
  3. Sep 16, 2015 #2


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    Science Advisor
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    Which time are you indicating with "t?" Fall time? Or, travel time of the splash noise? Or, total time?
  4. Sep 17, 2015 #3
    The time is from the time that the rock was dropped until the sound was heard.
  5. Sep 17, 2015 #4


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    Staff: Mentor

    Welcome to the PF.

    Divide it up into two times and two equations. Can you take a cut at doing that? :smile:
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