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Vector diagram - particle collision

  1. May 31, 2012 #1
    1. The problem statement, all variables and given/known data

    see attached image

    2. Relevant equations



    3. The attempt at a solution

    So I know as it is a VECTOR diagram it must either be B or C

    So I checked that 1, 2, 3, 4 all pointed in the correct directions and they do in both diagrams.
    I chose B (but at random) and the answer was C.
    Why is the answer C?

    thanks
     

    Attached Files:

  2. jcsd
  3. May 31, 2012 #2
    Hi jsmith!! :smile:

    Use the conservation of momentum, this tells you the initial total momentum should be equal to the final total momentum. In which of the options, do you see this??
     
  4. May 31, 2012 #3
    First of all, is this supposed to be a Classical Mechanics question or a Quantum mechanics question? Because if it is Classical mechanics, then the question is impossible. But in Quantum mechanics, it is possible.
     
  5. May 31, 2012 #4
    ??? classical mechanism

    why is it impossibel?
     
  6. May 31, 2012 #5
    I'm assuming the mass is constant?
     
  7. May 31, 2012 #6
    momentum is consereved in B??
     
  8. May 31, 2012 #7
    How is momentum conserved in B :confused:
     
  9. May 31, 2012 #8
    resultant momentum of both is in the same direciton, no?
     

    Attached Files:

  10. May 31, 2012 #9
    In classical mechanics, you have ##m_1v_{1i}+m_2v_{2i}=m_1v_{1f}+m_2v_{2f}## but that does not hold in the question, so I think it is a Quantum mechanics question...
     
  11. May 31, 2012 #10
    Uh nope, it isn't. And you can't be sure about the direction in B as the exact magnitude and direction of original aren't given.

    Also, direction isn't the only necessary factor. The magnitude remains same too. Observe C carefully.
     
  12. May 31, 2012 #11
    I just reaslied that i have to apply head-to-tail rule
    if I apply this it ALWAYS works for ALL questions that have bothered me in the past
    :)
     
  13. May 31, 2012 #12
    I believe classical mechanics does hold in the question....
     
  14. May 31, 2012 #13
    Yes!! That's it! :smile:
     
  15. May 31, 2012 #14
    Then I don't think I understood the question properly. What I understand of it is:

    $$v_{1i}=1$$
    $$v_{2i}=2$$
    $$v_{1f}=3$$
    $$v_{2f}=4$$
    $$m_1,m_2=\mbox{Constant}$$
     
  16. May 31, 2012 #15
    You didn't read the question properly o:)

    1, 2, 3, 4 are the momenta before and after collision, not the velocities.
     
  17. May 31, 2012 #16
    Oh! I didn't see that!
     
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