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Homework Help: Acceleration due to gravity of two objects

  1. Sep 10, 2008 #1
    1. The problem statement, all variables and given/known data
    Two objects are thrown from the top of a tall building. One is thrown up, and the other is thrown down, both with the same initial speed. What are their speeds when they hit the street?

    It's a multiple-choice question, and the choices are:

    a. The one thrown up is traveling faster.
    b. The one thrown down is traveling faster.
    c. They are traveling at the same speed.
    d. It is impossible to tell because the height of the building is not given.

    2. Relevant equations
    I don't know them, we're supposed to use logic.

    3. The attempt at a solution
    I think it should be a, because the one thrown up is gathering speed from the top of its arc and past the initial point. My study partner says c, because the ball going up cancels out the fall to the initial point.

    Any suggestions?
    1. The problem statement, all variables and given/known data

    2. Relevant equations

    3. The attempt at a solution
  2. jcsd
  3. Sep 10, 2008 #2


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    Homework Helper

    Welcome to PF.

    By symmetry you should understand in a uniform gravity field that the one thrown up at the same speed - roof level - will pass roof level at the same speed on the way down.

    Do you want to change your answer?
  4. Sep 10, 2008 #3

    So, if it passes the roof at the same speed it started at the roof, my study partner was right, because they both start at the roof at the same speed?

    That means that they have the same speed when they hit the ground because of V=vo+at, right?
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