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Provincial Exam: Simple momentum explosion question

  1. Jan 21, 2010 #1

    A 1.0kg physics puck is at rest when a small explosion breaks it into three pieces. A 0.50 kg piece, goes north at 10 m/s, a .3 kg piece goes east at 20 m/s. What is the magnitude of the momentum of the third piece.

    2. Relevant equations

    [tex]p = mv[/tex]
    Momentum Before = Momentum After

    3. The attempt at a solution

    So i know that the momentum before is zero, so the sum of the momentum on the x axis is zero, and the sum on the y axis is zero.

    Because the first two pieces are at right angles to eachother, i calculated the net momentum, or their resultant, and stated that the momentum of the third piece should be equal and opposite to maintain the law of momentum conservation.

    So i determined: the first piece had a momentum of 5 kg m/s north, the second, 6 kg m/s east.

    Plugged the values into the pythagorean theorum and got 7.8 kg m/s..

    Which is an answer on the sheet, but it's wrong. The correct answer is 3.3 kg m/s

    Could anyone tell me where i went wrong??

  2. jcsd
  3. Jan 21, 2010 #2
    *bump* :(