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Kinetic Energy Problem

  1. Oct 28, 2008 #1
    1. The problem statement, all variables and given/known data

    An internal explosion breaks an object, initially at rest, into two pieces, one of which has 1.6 times the mass of the other. If 25000 J is released in the explosion, how much kinetic energy does each piece acquire?

    2. Relevant equations



    3. The attempt at a solution
    I am not sure where to begin.
     
  2. jcsd
  3. Oct 28, 2008 #2

    LowlyPion

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    Here is a similar problem:
    https://www.physicsforums.com/showthread.php?t=267683
     
  4. Oct 28, 2008 #3
    Ok so m1=1.6m2
    How do I figure out v1?
     
    Last edited: Oct 28, 2008
  5. Oct 29, 2008 #4
    Would v1 be 1/1.6v2?
     
  6. Oct 29, 2008 #5

    LowlyPion

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    It depends on which piece is the heavier.

    What must be true in this problem?
     
  7. Oct 29, 2008 #6
    The heavier piece will have less velocity than the lighter piece.
     
  8. Oct 29, 2008 #7
    25000 J = 2.6/1.6 * 1/2 * m2v22
    So 25000J*.81=20250J for the lighter piece and 25000J-20250J=4750J for the heavier piece.
    Is that correct??
     
  9. Oct 29, 2008 #8

    LowlyPion

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    Not quite.

    They want the KE of the pieces. And the KE is mv2/2 not mv2

    Check your math.
     
  10. Oct 29, 2008 #9
    I am not sure what I am doing...that was just kinda of a guess.
     
    Last edited: Oct 29, 2008
  11. Oct 29, 2008 #10

    LowlyPion

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    So what does mv2/2 equal in your equation?

    Isn't that the KE of m2?

    Isn't that 1 part of what they asked?
     
  12. Oct 29, 2008 #11
    So 25000 J=2.6/1.6*1/2mv2v2^2 which is the same thing as 25000 J=2.6/1.6*mv2v2^2/2

    25000J=0.8125m2v2

    Am I on the right track?
     
    Last edited: Oct 29, 2008
  13. Oct 29, 2008 #12

    LowlyPion

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    Yes but 25000 J = 2.6/1.6 * 1/2*m*v2 = 2.6/1.6 * KE2

    Isn't the question "Find KE1 and KE2" ?
     
  14. Oct 29, 2008 #13
    Yes.
    So 1.625*KE2=25000
    KE2=15385J the lighter piece
    KE1=9615J the heavier piece
    ?
     
  15. Oct 29, 2008 #14

    LowlyPion

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    That's what it looks like.
     
  16. Oct 29, 2008 #15
    Great! Thanks ;)
     
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