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Homework Help: 2D Collisions

  1. Mar 26, 2013 #1
    1. The problem statement, all variables and given/known data

    A billiard ball moving at 5.40 m/s strikes a stationary ball of the same mass. After the collision, the first ball moves at 4.48 m/s at an angle of 34.0° with respect to the original line of motion. Assuming an elastic collision (and ignoring friction and rotational motion), find the struck ball's velocity after the collision.

    2. Relevant equations

    Conservation of momentum, conservation of KE

    3. The attempt at a solution

    Using conservation of momentum I got the final velocity of the second ball to be approximately 4.709

    This is due in about 10 minutes, which is probably not possible for me to do, so at this point I give up on trying to figure it out on my own and need a bit of help understand these concepts as a whole for future homework/exams.
  2. jcsd
  3. Mar 26, 2013 #2
    Hello and Welcome to PF,

    Could you please clarify as to where you are stuck in the problem?
  4. Mar 26, 2013 #3
    Thank you,

    and in all honesty I'm just having trouble setting things up. I understand the concepts of conservation of momentum and KE and where they do and don't apply, however it has always been a trouble for me applying direction to these sort of problems. I tried running through the notes my instructor provides both in-class and online help very little to not at all with this problem, as she barely mentioned changes in direction in collisions like this sort of problem.
  5. Mar 26, 2013 #4
    I assume you are capable of resolving a vector into mutually perpendicular components. Ask yourself this: What would be the direction of the net final momentum of the system? How would you find the direction of the resultant of two vectors? If the resultant of the two and one of the vectors are known could you find the other?
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