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Homework Help: Calculating the speed of P-waves.

  1. Sep 16, 2005 #1
    Any one any good at calculating equations?????

    Using the equation below,

    [tex]V_{p}=\frac{\sqrt{\frac{x+4}{3y}}}{p}[/tex]


    P = 3.4 x10³ Kg m¯³

    X = 1.6 x1011 N m¯²

    Y = 6.4 x1010 N m¯²

    I need to calculate the value of Vp and I need to give my answer in Km per second.


    Does anyone have any advice on how to do this??? :cry:
     
    Last edited: Sep 16, 2005
  2. jcsd
  3. Sep 16, 2005 #2

    Doc Al

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    Staff: Mentor

    Where did you get that equation? What are the units of the 3 and the 4 under the square root? (The 4 must have the same units as x, but what about the 3?)
     
  4. Sep 19, 2005 #3
    more like this

    it should really read like below, but couldn't get the formula right to put the equation in prop.

    x+4/3y

    this should be on the top line then its divided by the p.

    any idea's please any help will be usefull, cheers :cry:
     
  5. Sep 19, 2005 #4

    HallsofIvy

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    Science Advisor

    You do understand that this is just arithmetic don't you? But it's pretty complicated arithmetic!

    x is 1.6 x1011 so x+ 4= 1.6 x1011+ 4.

    What??? That's like 160000000000+ 4= 1600000000004!

    Since you only have 2 significant figures, that's 1.6 x1011 again!

    In other words, 4 is so small compared with 1.6 x1011 that adding it really doesn't make any difference. (If you had 1.6 x1011 dollars, 4 dollars wouldn't matter much!)

    Since we can ignore the "4", (x+ 4)/(3y) is just x/(3y).
    y= 6.4 x1010 so 3y= 18.4 x1010 and
    x/(3y)= 1.6 x1011/18.4 x1010= (1.6/18.4) x1011-10. Can you do that?

    Of course, taking the square root divides the power of 10 by 2 (I recommend you rewrite the number, if necessary, to make that power even!).
     
  6. Sep 21, 2005 #5
    Thank you for your help.

    Any ideas how to calculate the Meters squared into Km per second?
     
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