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Homework Help: Pls help me with this problem

  1. Jul 29, 2007 #1
    1. The problem statement, all variables and given/known data
    A stone is dropped from the top of a building. If it takes 5 seconds for the stone to hit the ground, how high is the building? What is the velocity just before it hits?

    2. Relevant equations
    d=Vit + 1/2[g(t^2)]
    Vf=Vi + gt

    3. The attempt at a solution
    =1m/s(5s) + 1/2[9.8m/s^2(5s^2)]
    =122.5m downward
    =0 + 9.8m/s^2(5s)
    =49m/s downward
  2. jcsd
  3. Jul 29, 2007 #2
    Where did you get the initial velocity from?
  4. Jul 29, 2007 #3
    that is the problem...cause that solution was given to us by our teacher...and i'm wondering how did she get it...
  5. Jul 29, 2007 #4


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    Staff Emeritus
    Science Advisor
    Gold Member

    If the stone is dropped that assumes that the initial velocity is 0. If it was stated the stone was thrown with an initial velocity of 1m/s then the solution would make sense.

    From what you have put though the answer is correct and the teacher hasn't included the initial velocity to get the height of the building in the calculation. Perhaps just an error on her part, teachers are humans too you know. :wink:
  6. Jul 29, 2007 #5
    -stacy libido
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