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Homework Help: Puck Collision

  1. Nov 5, 2007 #1
    1. The problem statement, all variables and given/known data

    Two identical pucks are on an air table. Puck A has an initial velocity of 2.6 m/s in the positive x-direction. Puck B is at rest. Puck A collides elastically with puck B and A moves off at 2.50 m/s at an angle of +16.3° above the x-axis. What is the speed and direction of puck B after the collision? (Take angles above the x axis to be positive and below to be negative.)
    _____ m/s at -73.7 °

    2. Relevant equations


    3. The attempt at a solution

    I got the angle but I have no idea what the speed would be. Does anybody have like a ball park figure of what it would be? because the answers i get dont even make sense.
  2. jcsd
  3. Nov 5, 2007 #2
    velocity is a vector so you find it by finding the resultant vector if you have the angle then you must have Vx and Vy, therefore you can find V
  4. Nov 5, 2007 #3
    no i dont have Vx and Vy, i just applied the physics of pool where hitting a ball on another ball will result in a total angle of 90 degrees. So i do not know where or how to find the V.
  5. Nov 5, 2007 #4
    In an elastic collision you will have conservation of momentum and energy. That gives you 3 equations to work with because you have momentum in both the x direction and perpendicular to it -- the y direction?
  6. Nov 6, 2007 #5


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    Homework Helper

    you've got the direction. just use a mass m for the puck. what is the total energy before the collision in terms of m. let vb be the velocity of puck B after the collision. what is the total energy after the collision in terms of m and vb...

    set the energy before = energy after.

    solve for vb.
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