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Homework Help: If the speed of sound is 330 m/s. How high is the cliff?

  1. Mar 20, 2007 #1
    Hello, I tried solving this but to no avail.
    Maybe someone could help me figure out the answer, thanks.

    A rock is dropped from a sea cliff and the sound is heard striking the ocean 3.0s later. If the speed of sound is 330 m/s. How high is the cliff?


    I've already tried about everything that I knew.
    I know that the time it takes the rock to fall to the bottom and the time it takes for the sound to travel back up to the person takes a total of 3s.

    I tried using the d=v1t + 1/2at^2 formula but that didn't work either.

    I've thought of and tried to use most formulas, but I don't know how to do this problem. Please help me.
    Last edited: Mar 20, 2007
  2. jcsd
  3. Mar 20, 2007 #2
    What have you tried so far? You need to show some work, and if this is homework it really belongs in the homework forum.
  4. Mar 22, 2007 #3
    Just remember that the time taken for the sound to reach your ears = 3 - the time taken for the rock to hit the water, and solve simultaneously.

    @hage: How is my answer wrong?
    Last edited: Mar 22, 2007
  5. Mar 22, 2007 #4


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  6. Mar 22, 2007 #5


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    Saplingg, I'll send you a PM.
  7. Mar 22, 2007 #6
    Hmmmm... I wonder if the problem is expressed incorrectly or if a teacher is just trying to make a point. Since you only have 2 significant digits for the time, the amount of time it takes makes no significant difference. In fact, using 3.00s for the time, and 9.81m/s^2, as well as 330m/s for the speed of sound, it still results in the same answer after rounding to three significant digits.
  8. Mar 23, 2007 #7
    I think if you drop the rock, you can assume that 3 second is the time the rock reaches the sea plus the time is needed for the sound to reach your ear so if we consider h as the height
    3= h/330+t
    and for t we have: h=1/2gt^2
    if we replace the t in the first equation from the second one
    we can solve it!
    is it ok?
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