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Help with conservation of energy

  1. Nov 8, 2007 #1
    1. The problem statement, all variables and given/known data
    Two billiard balls move of equal mass move at right angles and meet at the origin of an xy coorindate system. Ball A is moving upward along the y axis at 2.0m/s and ball B is moving to the right along the x axis with a speed of 3.7m/s. After the collision, assumed elastic, ball B is moving along the positive y axis . What is the final direction of Ball A and what is their speeds.

    2. Relevant equations
    Conservation of momentum :

    I know that the masses cancel as they are the same.
    But that still leaves me with 2 unknowns in that equation. Do I have to use trig functions to fing the velociy of ball B and then use the momentum to find velocity of ball A?? but then how do i find the direction of ball A

    3. The attempt at a solution
  2. jcsd
  3. Nov 8, 2007 #2
    In an elastic collision linear momentum and energy are conserved. You have two independent lines (x and y) so that gives you three equations ...
  4. Nov 8, 2007 #3
    O right sorry I forgot to write out the equation for the momentum along y. so in the x equation for example Vax= 0 and simiarly for the y equation? and is the third equation the kinetic energy one?? But I am sill confused as too how i find the direction of the A Ball.
  5. Nov 8, 2007 #4
    Don't worry about finding the direction of the A ball; if you find its velocity in the x direction and its velocity in the y direction ...
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