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Homework Help: Latent Hear

  1. Mar 10, 2010 #1
    1. The problem statement, all variables and given/known data
    A Bullet of ice at a temperature of 0 degrees celieus is fired into a target
    Assuming that all the impact energy is retained by the ice
    what impact velocity is needed to melt 68% of the ice

    2. Relevant equations

    1/2mv^2
    Q = ml
    3. The attempt at a solution
    i got..
    v^2 = 668000
    i doubt that is the correct answer
    can some show me the steps to work this out
     
  2. jcsd
  3. Mar 10, 2010 #2

    ideasrule

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    Why didn't you use the 68%? The kinetic energy turns into the energy needed to melt 0.68m, not m.
     
  4. Mar 11, 2010 #3
    um im still puzzled
    LOL
    can u show me the steps?
     
  5. Mar 11, 2010 #4

    ideasrule

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    Homework Helper

    I thought you used:

    1/2mv^2
    Q = ml

    and equated them to get:

    1/2mv^2=ml
    v^2=2l

    The statement 1/2mv^2=ml means "all the kinetic energy turns into the energy needed to melt the mass". However, only 68% of the mass melts, so the kinetic energy has to equal 0.68ml.
     
  6. Mar 11, 2010 #5
    oh i see....

    i got... 674 m/sec

    doesn't seem right

    Ek = 334800 x .68?
     
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