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F = MA 2011 # 14 (Creating a uniform sound)

  1. Jan 26, 2013 #1
    1. The problem statement, all variables and given/known data
    See:
    https://aapt.org/physicsteam/2012/upload/exam1-2011-1-3-answers_1.pdf
    Number 14


    2. Relevant equations
    None that come to mind


    3. The attempt at a solution
    I think this is a conceptual question where each needs to be more proportionally spread apart because it takes longer to reach the next object after colliding with the one before it.
     
  2. jcsd
  3. Jan 26, 2013 #2

    jedishrfu

    Staff: Mentor

    You could work it in reverse imagine you are accelerating upward and use the s=1/2 a t^2

    And so every second you are following a t^2 path which if you recall is something like:

    1,3,5,7 separation between points which is 1,4,9,16
     
  4. Jan 26, 2013 #3
    What is a t^2 path - where did you get those numbers (1,3,5,7) from?
     
  5. Jan 26, 2013 #4

    jedishrfu

    Staff: Mentor

    have you ever plotted y=x^2 with x=0,1,2,3,4 and get y=0,1,4,9,16 then if you take the differences between each point you get 1,3,5,7 right?
     
  6. Jan 26, 2013 #5
    Yes but how does that relate to this question? And why would you take the difference?
     
  7. Jan 27, 2013 #6

    jedishrfu

    Staff: Mentor

    If you look at the spacing of pointsfor D they follow the 1,3,5,7 sequence or if you number the points from the bottom you get 1,4,9,16 so right there you know you have a parabolic function.

    In contrast E tries to fool you as the points are spaced at 1,4,9,16 so might conclude that E is the answer.

    and A isn't spaced as a parabola and is backwards
    and B is evenly spaced so thats not a parabola
    and C is spaced like A but still isn't a parabola
     
  8. Jan 27, 2013 #7
    And how does a parobolic function signify that the sound is uniform?
     
  9. Jan 27, 2013 #8

    jedishrfu

    Staff: Mentor

    when things fall the follow s=1/2 a t^2 equation right? and thats a parabolic equation in t.
     
  10. Jan 27, 2013 #9
    Ok so that makes sense as to why its uniform?
     
  11. Jan 27, 2013 #10

    jedishrfu

    Staff: Mentor

    so whats left is for you to think about it a bit. You could even do the experiment and listen to the sound.
     
    Last edited: Jan 27, 2013
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