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Position when 2 objects pass each other

  1. Oct 18, 2007 #1
    1. The problem statement, all variables and given/known data
    An object is thrown downward with an initial speed of 4 m/s from a height of 99m above the ground. At the same instant, a second object is propelled vertically from the ground level with a speed of 25 m/s.
    The acceleration of gravity is 9.8 m/s^2.
    At what height above the ground will the two objects pass each other? Answer in units of m.


    2. Relevant equations
    [​IMG]

    3. The attempt at a solution
    Well I tried to find a common variable to plug in. I tried to plug in the position, then find time, then find the position, but it didnt work. Any help is appreciated.
     
  2. jcsd
  3. Oct 18, 2007 #2

    learningphysics

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    Can you show exactly what you did?
     
  4. Oct 19, 2007 #3
    What I did didn't work. I kind just mushed stuff together. I might as well have said "I didnt know where to start" because I didnt.
     
  5. Oct 19, 2007 #4

    learningphysics

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    the equation to use is:

    d = v1*t + (1/2)at^2

    now use d = X - Xo

    X - Xo = v1*t + (1/2)at^2

    so: X = Xo + v1*t + (1/2)at^2

    X is the height at any time t. Xo is the initial height.

    use this to get the displacement equations for each of the 2 objects...

    after you do that, set them equal... solve for t...
     
    Last edited: Oct 19, 2007
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