Find speed of two objects after collision

  1. 1. The problem statement, all variables and given/known data
    [​IMG]
    Puck A has a mass of 0.226 kg and is moving along the x axis with a velocity of 5.59 m/s. It makes a collision with puck B, which has a mass of 0.452 kg and is initially at rest. The collision is not head-on. After the collision, the two pucks fly apart with the angles shown in the drawing. Find the final speed of

    a) Puck A

    b) Puck B

    2. Relevant equations
    No idea



    3. The attempt at a solution
    No Idea


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    Where do I even start?
    1. The problem statement, all variables and given/known data



    2. Relevant equations



    3. The attempt at a solution
     
  2. jcsd
  3. G01

    G01 2,698
    Homework Helper
    Gold Member

    Chegg
    You have to show some work in order to get help here. Those are the rules. "No idea" doesn't cut it, sorry.

    You have to have SOME thoughts on the problem. What have you tried? What concepts does the problem involve?
     
  4. Well I do have some thoughts...
    I know that it has to do with momentum, and directions.

    I really just don't know where to start.. After I find the momentum, where would I go from there?
     
  5. Consider the relationship between the momenta before and after collision ...
     
  6. Will the both have the same momentum?
     
  7. That's what the law of conservation tells us ... and there are more than two (you wrote "both") momenta to consider.
     
  8. Ok, so how would you figure out what the momentum of the two are after the collision?
     
  9. p = mv

    Both p (momentum) and v (velocity) are vectors so it's a vector equation.

    Start with the horizontal momenta, one for A before and one each for A and B after. After must be the same as before (conservation!). You don't know the magnitude of the velocities of A and B after so you'll have to call them Va and Vb (or some such) and find another equation to find their values.

    I've got to go now.
     
  10. Ok, so how do you find out the velocity of A & B?

    So far I've come up with these equations:

    P=m*v
    = 0.226kg * 5.59m/s
    = 1.263314 kg*m/s

    Vay = Va sin 37 -- for A's Y direction
    Vax = Va cos 65 -- for A's X direction
    Vbx = Vb cos 37 -- for B's X direction
    Vby = Vb sin 65 -- For B's Y Direction

    So Va = Sqrt((Vax)^2+(Vay)^2)

    Just lost on how to find the velocity of Va and Vb...
     
  11. I'm not 100% sure but I think Ma*Va+Mb*Vb=Ma*5.59
     
  12. That just tells me the Vb is 0...
     
  13. Correct.

    Also correct. The suffixes a, b, x and y are a smart move. Helpful to use something like 1 for before the collision and 2 for after.

    Correct but not useful in this problem.

    Let M stand for the mass of A, 0.226 kg. How many M is the mass of B?

    Slightly modifying what you wrote above, the total momentum in the x direction before the collision can be written
    P1x = (V1ax * m1) + (V1bx * mb)
    = (5.59 * M) + (0 * 2M)
    = 5.59M

    Use your expressions for velocities after the collision (V2ax etc.) in an expression for the total momentum in the x direction after the collision:
    P2x = ...

    What is the total momentum in the y direction before and after the collision?
    P1y = ...
    P2y = ...
     
  14. That's only correct if the + sign indicates vector addition.
     
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