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Homework Help: Find the height of a free falling object

  1. Feb 15, 2015 #1
    1. The problem statement, all variables and given/known data
    An object falls freely, moving 60m in the last 2 seconds. Find the height at which it was dropped.



    2. Relevant equations
    Vf = 1/2(gt^2) + Vo(t)+ Yo
    g= 9.8m/s^2



    3. The attempt at a solution
    the object accelerates at 9.8m/s^2 . and the velocity would be 30m/s. (60 divided 2) so do you plug in 30m/s and the acceleration of gravity and solve for Yo? (the initial position)
     
  2. jcsd
  3. Feb 15, 2015 #2

    BvU

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    Dag KwamKwam, welcome to PF :smile:

    You want to check your equation -- or precisely describe what you mean with Vf. Otherwise the dimensions don't fit.
    To me it looks as if two equations from here have been squashed together. And you need both, I think.
     
  4. Feb 15, 2015 #3
    Thank you, Vf is the objects final velocity
     
  5. Feb 15, 2015 #4

    BvU

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    You still want to check your equation. On the left you have m/s, on the right you have m + m/s + m . Can't be right !
    Can you make sense of the expressions in the link I gave ?
     
  6. Feb 15, 2015 #5
    yeah I can. so my equations are V = Vo+ a(t) and X=Xo + Vo(t) + 1/2(at^2) instead of my first one?
     
  7. Feb 15, 2015 #6

    BvU

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    Very good. a(t) and V0(t) are confusing. Better write a t and V0 t or a ##\times## t and V0 ##\times## t

    Now you have these two equations you want to sort out how to apply them. What to fill in, how to choose t = 0 and x = 0 and such. Any ideas ?

    (bedtime for me, so others will have to help you further).
     
  8. Feb 15, 2015 #7
    so X0 = 60, t = 2 and a = -9.8 and V0is what we're searching for.
     
  9. Feb 15, 2015 #8

    haruspex

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    And X=?
     
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