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Homework Help: Conservation of Momentum in an Explosion

  1. Aug 2, 2015 #1
    1. The problem statement, all variables and given/known data
    During an explosion, a bomb explodes into 3 pieces. Two fragments, whose masses are 0.8kg and 0.5kg fly off with velocities of 10m/s and 16m/s respectively along the paths at right angles to each other. If the third fragment goes off with a velocity of 24m/s, then find its mass and direction w.r.t the first fragment.

    2. Relevant equations
    - Components ( u sin A and u cos A)
    - Conservation of momentum. The horizontal components=0 and the vertical components=0

    3. The attempt at a solution
    For M1
    horizontal component of velocity= 10 cos A
    vertical component of velocity= 10 sin A
    Horizontal momentum= 0.8 x 10cosA
    = 8cosA
    Vertical momentum=10sinA x 0.8
    = 8sinA

    For M2
    Horizontal component of velocity=16sinA
    Vertical Component of velocity= 16cosA
    Horizontal momentum= 8sinA
    Vertical momentum= 8cosA

    How do I find out the direction in which the third pieces moves in? Without the direction on the diagram I've drawn, I cannot split its velocity in component.
    Thanks in advance!
  2. jcsd
  3. Aug 2, 2015 #2


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    Gold Member

    You'll need to either include your diagram, or specify either "clock" or compass directions for us.
  4. Aug 2, 2015 #3


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    Momentum is conserved, right? And you know the final momentum of the first two pieces. If you assume that the bomb started at rest, what must be the final momentum of the third piece?
  5. Aug 2, 2015 #4
    Since momentum is being conserved.The momentum of the third particle will be anti parallel to the resultant of the momenta of the first and second particles.
  6. Aug 2, 2015 #5
    But why is the momentum anti parallel?
  7. Aug 2, 2015 #6
    Here's the diagram.

    Attached Files:

  8. Aug 2, 2015 #7
    3D or 2D?
  9. Aug 2, 2015 #8
    Because the bomb is initially at rest with a total momentum of zero.The momentum after the explosion should be zero too because there are no external forces acting on it.
  10. Aug 2, 2015 #9
    The question doesn't say. But I think it's 2D.
  11. Aug 2, 2015 #10
    Thank you! I get it now!
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