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Homework Help: Exploding Object fragments

  1. Oct 21, 2007 #1
    A 45.0-kg body is moving in the direction of the positive x axis with a speed of 217 m/s when, owing to an internal explosion, it breaks into three pieces. One part, whose mass is 6.0 kg, moves away from the point of explosion with a speed of 349 m/s along the positive y axis. A second fragment, whose mass is 2.5 kg, moves away from the point of explosion with a speed of 346 m/s along the negative x axis. What is the speed of the third fragment? Ignore effects due to gravity.

    I noticed right away that there might be components, so I came up with this:

    X direction: 45*217=2.5*-346+36.5x x=291.23
    Y direction: 45*217=6.0*349+36.5y y=210.15

    then i plugged those two values into the pythagorean theorem. I get 359.14 m/s, however the computer says I'm wrong. Could someone help me?
  2. jcsd
  3. Oct 21, 2007 #2


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    If the object is initially moving in the x direction only, the initial momentum in the y direction is zero since there is no component of velocity in that direction.
  4. Oct 21, 2007 #3
    whoops, thanks

    296.82 m/s is what the corrected formula yielded.

    The second part to the question is How much energy is released in the explosion? What is that exactly?
  5. Oct 21, 2007 #4


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    I would calculate the difference between the initial kinetic energy of the large mass, and the total kinetic energy of the three fragments after the explosion.
  6. Oct 21, 2007 #5
    okay, cool

    i go the right answer: 1.06x10^6 J

    I was just confused about how I should treat it since it broke apart. This problem was surprisingly easy.
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