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I'm confused by this concept 2-d motion dumb question

  1. Sep 13, 2016 #1
    1. The problem statement, all variables and given/known data
    A cart that is rolling at constant velocity on a level table fires a ball straight up. When the ball comes back down, will it land in front of the launching tube, behind the launching tube, or directly in the tube? Explain.

    2. Relevant equations

    3. The attempt at a solution
    Why does it land right back into the cart. That is super counterintuitive for me. I feel like the only forces on it if we don't include air friction is gravity. Therefore shouldn't it land behind the cart?
  2. jcsd
  3. Sep 13, 2016 #2


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    Suppose you are standing in the aisle of an airplane that is moving at 600mph and you jump up a couple of feet in the air. Where do you think you would come down? Why?
  4. Sep 13, 2016 #3
    In the same place. O this is without air friction right
  5. Sep 14, 2016 #4


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    The problem statement does not say if you should or shouldn't ignore air resistance. I would give answers for both cases.
  6. Sep 14, 2016 #5


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    In phinds' plane example, the air moves with the plane and there is no horizontal motion relative to the air to affect the landing spot when someone jumps straight up. In the demonstration below, there is horizontal motion relative to the air but the ball still lands in the cart. Therefore, air resistance can be safely ignored because the experiment says so.

  7. Sep 14, 2016 #6


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    Right[/quote]O this is without air friction right[/QUOTE]well, do YOU think there is any air friction in that example?
    Well, no, THIS experiment actually does NOT show that. If you look carefully you'll see that the ball lands an inch or two behind the hole from which it was released. Since it is a light plastic ball, the obvious inference is that this is (unintentionally) a demonstration of how air resistance DOES make a difference in some cases. He should have used a steel ball bearing for a better demonstration since that would have been far less affected by air resistance.
    Last edited: Sep 14, 2016
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