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How much kinetic energy is released

  1. Mar 26, 2015 #1
    1. The problem statement, all variables and given/known data
    A 6.0-kg object, initially at rest in free space, “explodes” into three segments of equal mass. Two of these segments are observed to be moving with equal speeds of 20 m/s with an angle of 60° between their directions of motion. How much kinetic energy is released in this explosion?

    a.2.4 kJ

    b.2.9 kJ

    c.2.0 kJ

    d.3.4 kJ

    e.1.2 kJ

    2. Relevant equations
    m1v1 + m2v2 + m3v3 = m1v1f + m2v2f + m3v3f
    K = 0.5*m*v^2

    3. The attempt at a solution
    The answer is c, 2000J, but I got 1500J and I don't know where I did wrong. Can anyone help me?
    My work is in the picture

    Attached Files:

  2. jcsd
  3. Mar 26, 2015 #2
    Nevermind I got it. Just made an algebric mistake..

    Attached Files:

  4. Mar 26, 2015 #3


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    Even so, herer's a tip: place the x-axis halfway between m1 and m2. That way py cancels. Less chance of error. But you do need cos(60) which at first you had 0 :smile: !
  5. Mar 26, 2015 #4
    Thanks for the tip!!
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