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Homework Help: Energy conversion- burning wood to lifting an object

  1. Sep 20, 2011 #1
    1. The problem statement, all variables and given/known data

    If the calorific value of wood is 16 MJ/kg and a match weights approximately 0.17 g, then (a)
    how much energy (in joules) is released by burning the wooden part of a single match? If all
    of this energy were applied to do work to lift a 60 kg human vertically, against gravity, then
    (b) how high could the person be lifted?


    2. Relevant equations

    W=F*d

    F=ma



    3. The attempt at a solution

    So for a. I was given the calorific value for a kg of wood. So I crossed multipled and divide.

    (16 MJ/kg*.00017kg) /1= 2720 J

    then for B.

    Joules can also be expressed in Nm
    using formula W=F*d ->W/F=d

    I was confused at first about the 80 kg because I assumed that was his weight but I am using that number as his mass. So found out that 80kg of mass= 588 N

    w=2720Nm F= 588 N

    2720Nm/588N= 4.626 m

    Now does that seem a lot to you? It did at first but now I am not sure.

    Please let me know if I am on the right track. This whole answer hinges on if I got the first part right... it seemed too easy so thats why i am second guessing myself...
     
  2. jcsd
  3. Sep 20, 2011 #2

    gneill

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    Staff: Mentor

    Looks good. Lot's of energy bound up in organic substances, which is why we burn coal and oil for energy.
     
  4. Sep 20, 2011 #3
    Yes, it seems reasonable. That's the problem with heat - there's a whole lot of it, but we can utilize only small fractions to make it do what we want.
     
  5. Sep 21, 2011 #4

    rude man

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    Homework Helper
    Gold Member

    Yeh - darn Carnot, Clausius & Kelvin and their 2nd law!
     
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