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Homework Help: Question about direction of heat

  1. Jan 31, 2010 #1
    If 2 object with different masses and different specific heat at different Temperature are put in water that have certain mass and temperature. If the heat loss is count by percent (that is, let's say 20% of heat is lost). Find the final temperature

    To solve this problem, I have to first determine the direction of the heat; that is, if i don't know which system gains energy and which system lose energy, then i will not know which q do i have to apply the 20% heat loss to.

    So

    q1 + q2 + q3 = q_loss

    where q_loss can either be:
    0.2(q1) --> if q1 is negative (object1 lose energy)
    0.2(q2) --> if q2 is negative ,,
    0.2(q3) --> if q3 is negative ,,
    0.2(q1+q2) --> if q1 and q2 are negative
    0.2(q2+q3) --> if q2 and q3 are negative
    0.2(q1+q3) --> if q1 and q3 are negative

    To find q_loss, we need to know which one is negative; we need to know the change in temperature (however, final temp is unknown). Therefore, is there another method to determine the direction of heat for each individual object without having to do trial and error method?

    I think there must be a way to know the direction without knowing the final temperature. However, my attempt has failed
     
  2. jcsd
  3. Jan 31, 2010 #2

    Matterwave

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    Science Advisor
    Gold Member

    Heat always flows from hotter objects to colder objects (temperature wise). I don't know if that's what you're really asking though...
     
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