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Homework Help: Newton's law of cooling question, no inital temperature given

  1. Apr 25, 2012 #1
    1. The problem statement, all variables and given/known data
    The temperature of an object has been lying at rest and cooling for sometime had been found to be 31oC. An hour later, the same object was found to be 30oC. The room was also What was the initial temperature of the object, assume newton's law of cooling applies.

    2. Relevant equations
    newton's law of cooling

    [itex]\frac{dT}{dt}[/itex] = k (T - Ts) where:

    Ts = ambient temperature
    T = the temperature at anytime
    k = constant of proportionality

    3. The attempt at a solution
    Ok, normally when I do a newtons law of cooling question, I start off with the inital temperature followed by a temperature at an "X" time. And then I would convert the formula into it's exponential form i.e. y = Aekt+c. then I would use the initial temperature (or the temperature when t=) to cancel out one of the variables. However, I'm trying to find the inital temperature, so this method won't work for me anylonger and I'm not sure how to proceede :confused:

    Thanks guys/gals, any help will be greatly appreciated :biggrin:
  2. jcsd
  3. Apr 25, 2012 #2


    Staff: Mentor

    "The room was also" - what? Where's the rest of this sentence?
  4. Apr 25, 2012 #3
    Sorry, the room was also found to be 20 degrees celsius
  5. Apr 27, 2012 #4
    Take the initial temperature to be 31°C at t=0. The time spent lying at rest in the room doesn't matter before the temp was measured.
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