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Homework Help: Help with a formula

  1. Sep 22, 2005 #1
    I need to derive this formula:

    x = (sqrt of 2h/g)v

    from these two equations:

    h = .5gt^2

    x = vt


    Thanks... just can't figure this out!
     
  2. jcsd
  3. Sep 22, 2005 #2
    do you mean [tex] \sqrt{\frac{2h}{g}} v [/tex]

    Start off with the first equation. Replace what can be replaced in this equation. Rearrange and you're there!
     
    Last edited: Sep 22, 2005
  4. Sep 22, 2005 #3
    yes, this is the formula, it was for a lab so we were using x as a distance
     
  5. Sep 22, 2005 #4

    TD

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    Rewrite the first equation for t, I took the positive root:

    [tex]h = \frac{{gt^2 }}
    {2} \Leftrightarrow t^2 = \frac{{2h}}
    {g} \Leftrightarrow t = \sqrt {\frac{{2h}}
    {g}} [/tex]

    All that's left is substituting it in [itex]x = vt[/itex]
     
  6. Sep 22, 2005 #5
    but there is no way to combine the x=vt with it?
     
  7. Sep 22, 2005 #6

    TD

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    That's what you have to do now. Substitute the expression we found for t in the formula x = vt...
     
  8. Sep 22, 2005 #7

    Tom Mattson

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    Yes, there is. Take [itex]x=vt[/itex] and solve for [itex]t[/itex], then substitute.
     
  9. Sep 22, 2005 #8
    Are you kiddin' me, buddy? How about [tex]t = \frac{{x}}
    {v} [/tex]
     
  10. Sep 22, 2005 #9
    but i need to derive this formula:

    x = (sqrt of 2h/g)v

    from these two equations:

    h = .5gt^2

    x = vt


    i still dont understand how to do that
     
  11. Sep 22, 2005 #10

    Tom Mattson

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    The complete solution is right here in this thread.
     
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