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Collision between falling body and body shot upwards

  1. Sep 1, 2009 #1
    Hi this is my first post thanks to who ever contributes!

    1. The problem statement, all variables and given/known data
    A man drops a ball from the top of a 22m building. At the same instant his friend below throws a ball upwards at 22 m/s. What distance from the ground do the two balls meet.

    Ball A
    -------
    v1 = 0 m/s
    a = 9.8m/s down
    t=?
    d=?

    Ball B
    --------
    v1 = 22 m/s up
    a = 9.8 m/s down
    t = ?
    d = ?


    This assumes that ball A was dropped right at 22m and the other ball was thrown from ground level. Air resistance is negligible.

    My attempts have all failed my general approach was to solve for time that they hit at and then use that to find the distance one of the balls traveled. We are to use basic equations relevant to kinematics, force or energy (no calculus related stuff). Any help would be much appreciated

    Jasper
     
  2. jcsd
  3. Sep 1, 2009 #2

    Hootenanny

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    Welcome to Physics Forums.

    HINT: In terms of the balls' displacement, what does a 'collision' mean?
     
  4. Sep 1, 2009 #3
    well wouldn't a collision be when the displacements overlap?
     
  5. Sep 1, 2009 #4

    Hootenanny

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    If the balls collide at a height d0 above the ground, then the displacement of ball B is d=d0. What is the displacement of ball B?
     
  6. Sep 1, 2009 #5
    If you meant what is the displacement of ball a then it is d = 22 - d0 right?

    hmm wait I think i know what to do now I will post my result
     
  7. Sep 1, 2009 #6

    Hootenanny

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    Indeed I did and that is correct. :smile:
     
  8. Sep 1, 2009 #7
    I dont know what to do with time as all my formulas ask for it any tips would be nice
     
  9. Sep 2, 2009 #8

    Hootenanny

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    My hint is pretty much the same as for the displacement: the balls must collide at the same time. You should be able to write down two equations, one force each ball. Each equation should have two unknowns - time and displacement (don't forget to use the previous hint for displacement). Now, you have two equations with two unknowns - how would you usually go about solving this type of problem?
     
  10. Sep 2, 2009 #9
    Ya i figured it out thanks alot
     
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