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Gravitational acceleration problem

  1. Oct 27, 2014 #1
    1. The problem statement, all variables and given/known data
    Alice and Bill are at the top of a building. Alice throws her ball downward. Bill simply drops his ball. Which ball has the greater acceleration just after release?

    2. Relevant equations
    force, F=ma and F=mg

    3. The attempt at a solution
    Alice: F=ma+mg=m(a+g)
    Bill: F=mg
    Alice's ball has a greater acceleration.
    I AM WRONG. WHY?
     
  2. jcsd
  3. Oct 27, 2014 #2

    gneill

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    Staff: Mentor

    After Alice releases the ball, what's producing that acceleration "a" that you put in your equation?
     
  4. Oct 28, 2014 #3
    Because Alice throws instead of releases, an extra force is exerted downwards?
     
  5. Oct 28, 2014 #4

    gneill

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    Staff: Mentor

    Bill drops, Alice throws. But both release, otherwise they'd still be holding onto their balls. You're meant to consider the portion of the trajectories when they are no longer in contact with their ball.
     
  6. Oct 28, 2014 #5
    The acceleration for both of them should be the same.
    An acceleration is produced only when there is an external forces is applied.
    after release, the only force on the balls is tat of gravity.
    Thus the acceleration will be the same for both of them.

    Alice's ball has more acceleration only during the time when she is throwing the ball and excerting force, she gave it an initial velocity. After the ball leaves her hand, only gravity acts on it.
     
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