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Homework Help: What is the kinetic energy of the piece of mass

  1. Apr 28, 2007 #1
    1. The problem statement, all variables and given/known data
    A body, initially at rest, explodes into two pieces of mass 2M and 3M respectively, having a total kinetic energy E.
    What is the kinetic energy of the piece of mass 2M after the explosion?


    2. Relevant equations
    0.5mv²=K.E


    3. The attempt at a solution
    The velocity of the 2 pieces of objects is different,how do i calculate?
    Can anyone guide me on how to start?
    0.5(2m)(v_1)² + 0.5(3m)(v_2)²=E
    How do i proceed?
    Thanks for reading,thinking,replying.
     
  2. jcsd
  3. Apr 28, 2007 #2

    Doc Al

    User Avatar

    Staff: Mentor

    Hint: During an explosion, what physical quantity (if any) of all the pieces is conserved?
     
  4. Apr 28, 2007 #3
    Solution

    using conservation of momentum,
    0=2mu + 3m(-v)
    2mu=3mv
    2u=3v
    u=3v/2

    Total K.E
    =1/2(2m)(3v/2)² + 1/2(3m)(v)²
    =15/4(m)(v²)
    =E

    K.E for mass of 2m:
    1/2(2m)(3v/2)²
    =9v²m/4

    Hence,K.E for 2m is 3m/5.
    Okies thanks.
     
  5. Apr 28, 2007 #4

    Doc Al

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    Staff: Mentor

    You mean KE = (3/5)E.
     
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