1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

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



    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


    User Avatar

    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

    User Avatar
    Homework Helper
    Gold Member

    Yeh - darn Carnot, Clausius & Kelvin and their 2nd law!
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook