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Homework Help: Momentum and Collision

  1. Oct 23, 2005 #1
    Can't seem to get this right

    M1 = 7.0kg
    M2 = 4.5kg
    M3 = Mtotal - (M1+M2)

    Isn't it simply adding up momentum vector of M1, and momentum vector of M2 then the
    resultant will be momentum of M3?

    If so, then you get a right angle triangle.

    You know momentum of both sides and just by using pythagoras you can find
    momentum of M3, then just divided by the mass then you can get the velocity right?
  2. jcsd
  3. Oct 24, 2005 #2


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    You have to subtract the resultant from the original momentum vector of the bullet to get M3.

  4. Oct 24, 2005 #3
    I'm not really sure what you mean by that, could you explain it again thanks
  5. Oct 24, 2005 #4


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    Sorry I did not notice your formula M3 = Mtotal - (M1+M2) before. I wanted to say the same - you should subtract the resultant of M1 and M2 from Mtotal to get M3, and I ment that Mtotal is momentum of the bullet before exploding.

    M3 = Mtotal - (M1+M2).

  6. Oct 24, 2005 #5
    hm...Okay..i think this problem should be solve by components, but can i have some hints on how to use component methods?
  7. Oct 24, 2005 #6
    Use conservation of momentum...?
  8. Oct 25, 2005 #7


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    The total momemtum which is equal to the momentum the bullet had just before the explosion is 32*215i as the piece moves along the positive x axis. The momentum of the 7 kg piece is 7*310j as the piece moves along the positive y axis. The momentum of the 4.5 kg piece is -4.5*370i.
    The sum of the x components is the same before and after explosion, and the same holds for the y components.
    Calculate the components of M3. Determine the magnitude and divide by the mass of the third piece to get the speed as you have written down in your first letter.
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