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Homework Help: Throwing a ball from a cart

  1. Nov 20, 2012 #1
    1. The problem statement, all variables and given/known data
    You are standing on a frictionless cart which is at rest. At to you throw a ball to the left,
    with momentum p, at a wall on the left that is attached to the cart. At t1 the ball bounces off the wall, with the same momentum.
    a. What happens to the cart between to and t1?
    b. At time t2 you catch the ball. What happens to the cart between t1 and t2?
    c. What happens to the cart after time t2?

    2. Relevant equations

    3. The attempt at a solution
    When standing on the cart, and throwing a ball on a wall attached to the cart, I would think it depends on the weight of the person and the ball but we are not given that data. I think for part a, the cart would move to the left from the force of the ball.

    For part b, I think the cart would move to the right due to momentum of the ball, since you would be acting like a second wall on the right receiving the ball.

    For c the cart would stand still.

    Thanks for your help.
  2. jcsd
  3. Nov 21, 2012 #2


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    In (a), the ball is thrown to the left. Which way will the cart tend to move?
  4. Nov 29, 2012 #3
    if you stand on a skateboard( say totally frictionless) and push a wall with momentum p, which way will the board go?

    You talk about the weight not being given, it is irrelevant as the same momentum of the ball is always the change that occurs, regardless of the initial mass... Try think of a cannon, which fires a cannonball, in which direction does the canon move when the ball is fired?
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