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Homework Help: Heat problem

  1. May 29, 2006 #1

    This problem has been killing me...

    The Q is the following: A canon fires a canon ball which weighs 50 grams vertically at an initial speed of 600 m/s. 3 Km on top of the point where it was fired, the speed is only 50 m/s. calculate the heat during the canon ball rise.

    I dont know how to use the kinetic formula in function with the energy formula, any help would be appreciated!
  2. jcsd
  3. May 29, 2006 #2
    The canon ball has a certain amount of kinetic energy from the start and a certain kinetic energy when the speed is 50 m/s (which is less). Some of the kinetic energy has been transformed to potential energy. The rest of the energy has been "lost" as heat etc.

    Start: [tex]W_k[/tex]
    Finish [tex]W_k + W_p + W_h[/tex]

    Lets call the heat energy [tex]W_h[/tex] in this case although it isn't exactly correct index.
  4. May 29, 2006 #3
    Thanks for clearing things up, Mattara.

    So what would we eventually have to do to find Q, the heat produced?
  5. May 29, 2006 #4


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    Using Mattara's notation Q = Wh.

  6. May 29, 2006 #5
    so it would be Wh + Wp = -Wh ?
  7. May 29, 2006 #6


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    Not quite, intially you have some kinetic energy. At the 'end' you have some kinetic energy, some potential and the rest as heat, therefore;

    Initial Kinetic = Final Kinetic + Potential Energy + Heat

    [tex]\frac{1}{2}mv_{i}^{2} = \frac{1}{2}mv_{f}^{2} + mgh + Q[/tex]

    Can you go from here?

    Last edited: May 29, 2006
  8. May 29, 2006 #7
    hehe thanks Hootenanny
    Actually, i meant Wk + Wp= -Wh, the former Wh was a typo...

    But everything is clear now, thanks a lot to both of you!
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