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Principle of conservation of momentum question

  1. Jan 25, 2013 #1
    1. Somebody help explain how to do this for me, am not looking answer, an explanation so i can solve it would be great.

    A space vehicle traveling at a velocity of 7000km/h separates into two sections of mass 1100kg and 200kg. the two parts continue moving in the same direction with the lighter section moving at 10000km/h.

    Determine the velocity of the heavier section after separation
    The change in the total kinetic energy of the system



    2. I know to use the conservation of momentum (M1U1 + M2U1 = M1V1 + M2V2), but since there are three values for mass am not sure where to begin.



    3. any attempt i have made has been unsuccessful

    Cheers :)
     
  2. jcsd
  3. Jan 25, 2013 #2

    Doc Al

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    What's the mass and velocity of the space vehicle before it breaks up?
     
  4. Jan 25, 2013 #3
    the space vehicle is traveling at 7000km/h. i don't know the mass of it but wouldn't it be the sum of the sections so 1100+200=1300kg
     
  5. Jan 25, 2013 #4

    Doc Al

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    Exactly. So now you have one side of the momentum conservation equation. Set the initial momentum (of the intact vehicle) equal to the sum of the momenta of the sections after it breaks up.
     
  6. Jan 25, 2013 #5
    So if momentum is f=mv
    Would the momentum of the intact vehicle be (200x10000)+(1100x v?)
    Am still not sure about this
     
  7. Jan 25, 2013 #6

    Doc Al

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    The momentum of the intact vehicle is its mass (which you figured out already) times its velocity (which is given).
     
  8. Jan 25, 2013 #7
    So the momentum of the intact vehicle is 1300x7000=9100000
    Does that mean the sum of the momentums of the separate parts equal the momentum of the intact vehicle.
     
  9. Jan 25, 2013 #8

    SteamKing

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    That's what conservation of momentum is about.
     
  10. Jan 25, 2013 #9

    Doc Al

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    Exactly. When something is "conserved" that means it stays the same. The total momentum of the of the vehicle (or its parts) doesn't change when it breaks up.
     
  11. Jan 25, 2013 #10
    Is the answer 6454km/h
     
  12. Jan 25, 2013 #11

    Doc Al

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    Looks right.
     
  13. Jan 25, 2013 #12
    Then would the change in kinetic energy of the system be the kinetic energy of the intact vehicle minus the kinetic energy of the heavier of the two separate bits?
     
  14. Jan 25, 2013 #13

    Doc Al

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    Not exactly. The change in KE is the total KE after the break up (both pieces) minus the initial KE (of the intact vehicle).
     
  15. Jan 25, 2013 #14
    Thanks good help
     
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