Energy conversion- burning wood to lifting an object

  • Thread starter jongood
  • Start date
  • #1
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Homework Statement



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?


Homework Equations



W=F*d

F=ma



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...
 

Answers and Replies

  • #2
gneill
Mentor
20,925
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Looks good. Lot's of energy bound up in organic substances, which is why we burn coal and oil for energy.
 
  • #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.
 
  • #4
rude man
Homework Helper
Insights Author
Gold Member
7,931
822
Yeh - darn Carnot, Clausius & Kelvin and their 2nd law!
 

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