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Homework Help: Elastic collision in 2-d.

  1. Mar 23, 2010 #1
    1. The problem statement, all variables and given/known data
    Consider an elastic collision (ignoring friction and rotational motion). A queue ball initially moving at 2.9 m/s strikes a stationary eight ball of the same size and mass. After the collision, the queue ball’s final speed is 1 m/s. Find the queue ball’s angle with respect to its original line of motion.
    Answer in units of ◦.

    2. Relevant equations
    I can't seem to figure out how you're supposed to get an angle for this, if none is given.

    3. The attempt at a solution
    in 1-d the equation would be something like m1v1+m2v2=(m1+m2)*V. In 2-d, I assume you need a trig function, but how is that useful with no given angle?
  2. jcsd
  3. Mar 23, 2010 #2


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    Welcome to PF!

    Hi LTZach ! Welcome to PF! :wink:
    (btw, it's a cue ball! :wink:)

    Call the angle θ, and find three equations, for momentum in the x and y directions, and for energy.

    What do you get? :smile:
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