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Calorie Joule and mass

  1. Sep 22, 2014 #1
    Lets suppose we have 2000 kcal and we want to translate it joule.
    1 calorie is 4,2 J/gC isnt it so I think it will be 8400000 g m^2/s^2 But my teacher says its 8400000 kg m^2/s^2
    Which one is true
    Thanks
     
  2. jcsd
  3. Sep 22, 2014 #2
    Note: Here (4,2 J/gC) J is joule g is grams and C is celcius
     
  4. Sep 22, 2014 #3

    jtbell

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    Staff: Mentor

    No, 1 cal = 4.2 J (to one decimal place).

    You're thinking of the specific heat of water, which is 4.2 J/(g·°C) = 1 cal/(g·°C).
     
  5. Sep 22, 2014 #4
    Then let me clear Q=mcT and W=mgh so If we takes m we get Q/cT=W/gh If we write the unit form cal cal^-1 g C^-1 C we get g which it grams
    and the other side kg m^2 s^-2 s^2 m^-1 m^-1 then we get kg.It does not match.and I think its a problem
     
  6. Sep 22, 2014 #5

    jtbell

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    Staff: Mentor

    You're getting grams for the m from the first equation because you're using the specific heat per gram. Use the specific heat per kilogram instead: 4200 J/(kg·°C).
     
  7. Sep 22, 2014 #6
    Thanks I understan it
     
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