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Explosion Problem

  1. Dec 11, 2008 #1
    1. A projectile of mass 50 kg moving horizontally at 100m/s explodes into three pieces. Two pieces fly off vertically while a third continues horizontally at 150m/s (neglect gravity).

    What is the kinetic energy of the horizontally moving piece?



    2. Relevant equations

    KE=(1/2)mv^2
    W=∆KE
    W+KEi + PEi =KEf + PEf
    PE=mgh

    3. The attempt at a solution

    W=∆KE
    =(1/2)mvf^2-(1/2)mvi^2

    But I got incorrect answer. The correct answer is 375000 J
     
  2. jcsd
  3. Dec 11, 2008 #2
    This is a good problem. Does the mass break apart equaly because I keep getting half of the KE (187500J) I am doing .5(50/3)(150)^2. Anyone have any input
     
  4. Dec 11, 2008 #3
    The problem does not say, but that is the number I kept getting as well. 1875000 is half of 375000, but I am not sure if that is relevant to what we are doing wrong.
     
  5. Dec 11, 2008 #4

    LowlyPion

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    Homework Helper

    This looks like a Center of mass problem doesn't it?

    What you know is that at the moment of explosion you have 2 pieces that fly off, presumably 1 up and the other down of indeterminate mass and velocities in the vertical direction. But the piece of interest continues horizontally only faster.

    So ... don't you know that the center of mass is continuing at 100 m/s and now the horizontal piece is moving at 150 m/s?

    How must you balance that out such that the center of mass continues at the original 100 m/s, because that's what it will be doing won't it?
     
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