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Homework Help: Three Piece explosion

  1. Oct 17, 2004 #1
    A firecracker in a coconut blows the coconut into three pieces. Two pieces of equal mass fly off south and west, perpendicular to each other, at 20 m/s. The third piece has twice the mass as the other two.What is the speed of the third piece?

    really boggled, no masses are given? i thought since the mass is double then the speed would be half of the speed of the 1st and 2nd pieces? anyone have an equation to help me out?
  2. jcsd
  3. Oct 17, 2004 #2
    Resolve the momentums in the X and Y directions assuming the body is initially at rest:

    [tex]\sum m_i v_i = 0[/tex] Here's the X direction (assuming east/west are the postive/negative x axis):

    [tex] -20m + 2mv_x = 0[/tex]

    and in the Y direction:

    [tex] -20m + 2mv_y = 0[/tex]

    It's easy to see what [tex]v_x[/tex] and [tex]v_y[/tex] are.
  4. Oct 18, 2004 #3
    still dont understand, what do i put for the masses?
  5. Oct 18, 2004 #4
    It doesn't matter what the masses are. The ratios are given. The masses will cancel out later once you have the relationship worked out.
  6. Oct 18, 2004 #5
    so Vx = 10 and Vy = 10? after i solved in the equations
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