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Simple thermodynamics

  • Thread starter ashvuck101
  • Start date
  • #1
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Homework Statement



6. Cameron burns a 0.5g peanut beneath 75g of water, which increases in temperature from 22 ºC to 40 ºC
a. Assuming 40% efficiency, what is the food value, in J, of the peanut?
b. What is the food value in J per gram?

Homework Equations


q=mCt


The Attempt at a Solution



i just wanted to know does question a mean i take 40% from the calculated joules???
 

Answers and Replies

  • #2
370
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No, it's not, what it's saying to you is that the energy given off by the peanut to heat up the water is only 40% of the total energy given off in combustion, you need to work out the 100%. (was confused there for a sec :D)
 
  • #3
181
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No. It means only 40% of the peanut's energy goes into the water
 
  • #4
27
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what so how am i meant to calulate the other 60% thats not possible???
 
  • #5
370
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Of course it's possible, that's like me saying to you;

You have 4 apples, which is 40% of the total number of apples from the bag, how many apples were in the bag?
 
  • #6
27
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er could you put that to me algerbarically please... i mean it makes sence if it was 50% all you do is double it
 
  • #7
27
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could it be .4x=(Joules calulated)???
 
  • #8
370
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0.0

From 50% to 100% you times by 2....

From 40% to 100% you times by...

And ^ yes you're right.
 
  • #9
181
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:smile:
Of course it's possible, that's like me saying to you;

You have 4 apples, which is 40% of the total number of apples from the bag, how many apples were in the bag?
Beat me to it again.
Although I considered replying earlier
in similar vein I just couldn't bear to do it.

David
 
  • #10
370
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lawl =D
 

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