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Homework Help: Momentum Question

  1. Oct 25, 2013 #1
    Hi Everyone

    I would really appreciate some help with a momentum question; I don't want the whole answer, just the first step would be great!

    I have attached the diagram. A white pool ball is rolling along the pool table and strikes a stationary black ball. The white ball's initial mass and velocity is given (black ball's mass is the same), so initial system momentum is simple.

    The question wants the x and y momentum components for each ball after collision. But no further angles / velocities are given (angles are not 45 deg) and diagram given is not to scale - so I don't even know where to start!

    The previous question at least gave one angle and one velocity,so that was simple enough. Is the question flawed, or can someone please assist me just to get started - then I can finish the rest myself?

    Attached Files:

  2. jcsd
  3. Oct 26, 2013 #2


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    Is this problem from your textbook?
  4. Oct 26, 2013 #3


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    Gold Member

    Perhaps the answer is expected to be expressed in terms of the missing values. That's the best you can do with the given information.
  5. Oct 26, 2013 #4


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    Have you applied conservation of momentum to this problem?
  6. Oct 26, 2013 #5
    I think SteamKing is correct. Momentum of each ball after collision is half of momentum of white ball before the collision. Then use trig to calc x,y components.

    Why do you think the angles are not 45 degrees? Is that what the textbook says?
  7. Oct 26, 2013 #6
    Hi All

    I'm working through problems in preparation for the exams. The after collision individual momentums are are not half of the starting value, and the angles (from memory - I'm not at home) were around 53 deg for the white and I can't remember the black.

    I'm beginning to wonder if there isn't a value missing in the text question.
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