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The mechanical Equivalent of heat: total increase in temperature of the water?

  1. Nov 30, 2011 #1
    1. The problem statement, all variables and given/known data
    If in Joule's paddle wheel experiment a block of mass 10 kg is allowed to fall through 22.5 meters and the mass of the water is 50 grams. What is the total increase in temperature of the water?



    Can your value of J be used for determining how much mechanical energy can be produced from a specified amount of thermal energy?

    2. Relevant equations
    Im not sure how to start the problems and do not know what to do could someone please help and explain them to me
     
  2. jcsd
  3. Nov 30, 2011 #2

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    What's the formula for potential energy (something with mass and height in it)?
    And for thermal energy (something with mass and temperature in it)?
     
  4. Nov 30, 2011 #3
    PE=mgh
    Thermal energy= mct

    what do I do from there?
     
  5. Nov 30, 2011 #4

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    Good! :smile:

    What would m be in this problem?
    And g?
    And h?

    What would m be in this context?
    Do you have a value for c?
    How does t fit into your problem?
     
  6. Nov 30, 2011 #5
    m=10 kg
    g=9.8 m/s^2
    h=22.5 m
    ___________
    m=50 g
    c=4185.8 kg c
    t= Im not sure...
     
  7. Nov 30, 2011 #6

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    Right!

    Now there is something called conservation of energy.
    When your block falls, its potential energy has to go somewhere.
    It is converted into heat.
    What do you think the relation would be between the potential energy and the thermal energy?

    As for "t".
    What is it exactly that the problem asks you to calculate?
     
  8. Nov 30, 2011 #7
    the potential energy equals the thermal energy?
    the problem is asking for the total increase in temperature...
     
  9. Nov 30, 2011 #8

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    Exactly!

    Yes. And "t" is the symbol for the change in temperature.

    So...?
     
  10. Nov 30, 2011 #9
    ohhh ok i got it Thank you!
    could you explain the second question now lol your very helpful
     
  11. Nov 30, 2011 #10

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    What is J?
    And what are your thoughts on it?
     
  12. Nov 30, 2011 #11
    J is mgh/mct

    My book does not say anything about it, it just gives an equation so im not sure...
     
  13. Nov 30, 2011 #12

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    Okay, so you can calculate J, can't you?

    Can you put into words what J signifies?
     
  14. Nov 30, 2011 #13
    J means Joules... I thought it was only a unit...
     
  15. Nov 30, 2011 #14

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    Yes, J is usually the unit joule of energy.
    That's why I asked, because the way J is used in your problem description suggests that J is used for something else.....?
    Where did your formula for J come from?
     
  16. Nov 30, 2011 #15
    My physics book... its a conceputal problem. Yeh I was confused because it didnt say where that came from.
     
  17. Nov 30, 2011 #16

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    Conceptual problem or not, symbols always need to be defined before you can talk about concepts.
    Is it defined as the formula you gave then?
     
  18. Nov 30, 2011 #17
    My book says thats how you solve for J, so yes.
     
  19. Nov 30, 2011 #18

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    Can you put into words what the formula means then?
     
  20. Nov 30, 2011 #19
    Yes it is defined as the formula
     
  21. Nov 30, 2011 #20

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    So what's in the nominator of the formula? And what's in the denominator?
    Do you recognize those?
     
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