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What is the momentum and velocity of each ball after the...?

  1. Mar 26, 2016 #1
    1. The problem statement, all variables and given/known data
    A 3.50 kg ball with a velocity of 10.00 m/s collides with a stationary ball with a mass of 5.00 kg. After the collision, the first ball travels at a 42.6 degree angle from its original path, while the second ball travels at a -26.7 degree angle from the other ball's original path.

    1) What is the momentum of each ball after the collision?

    2) What is the velocity of each ball after the collision?

    2. Relevant equations


    3. The attempt at a solution
    1) p = 3.50 kg x 10.00 m/s = 35.00 Ns

    2) v = (3.50 kg)(sin42.6) + (5.00 kg)(sin-26.7) = -8.44 m/s

    I know that it's wrong, but I'm not sure how to solve these two problems. Can someone please help?
     
  2. jcsd
  3. Mar 26, 2016 #2

    mfb

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    That is the initial momentum of ball 1.
    kg and m/s are not the same. You cannot just exchange units like you want.

    What is conserved in the collision?
     
  4. Mar 26, 2016 #3
    momentum is conserved and is the initial momentum what i need? how do i find the other ball's momentum?
     
  5. Mar 26, 2016 #4

    mfb

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    You need the initial momentum, sure - as momentum is conserved, the final momentum will be the same. That gives you some relations for the speeds of the balls.
     
  6. Mar 26, 2016 #5
    i'm still really confused on how to solve this
     
  7. Mar 26, 2016 #6

    haruspex

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    Momentum is a vector, so has direction. The momentum you calculated has the direction of the original movement of the 3.5kg ball.
    If after the collision the velocities are u and v, what is the momentum in that direction? What is the momentum perpendicular to that direction? What two equations can you write?
     
  8. Mar 26, 2016 #7
    would you use m1v1=m2v2? and would the momentum of both of the balls be 35.00Ns?
     
  9. Mar 27, 2016 #8

    haruspex

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    The total momentum of the two balls, in the original direction of motion of the first ball, is 35Ns, yes.
    Write that as an equation with unknowns for the two speeds.
    What about momentum in the perpendicular direction?
     
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