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Homework Help: What was the temperature of the object?

  1. Jan 12, 2015 #1
    1. The problem statement, all variables and given/known data
    An object is placed in a room where the temperature is 20 degrees Celsius. The temperature of the object drops by 5 degrees Celsius in 4 minutes and by 7 degrees Celsius in 8 minutes. What was the temperature of the object when it was initially placed in the room?

    2. Relevant equations
    Newton's law of cooling: T(t)=Ta+(To-Ta)e^(-kt)

    3. The attempt at a solution
    I know that I need to solve for To, which is the initial temperature but I don't know what to do.
  2. jcsd
  3. Jan 12, 2015 #2


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    Rewrite Newton in terms of delta T and see if that gives you any ideas.
  4. Jan 12, 2015 #3
  5. Jan 12, 2015 #4


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    When t= 4 min, T(4)= Ta+ (To- Ta)e^(-4k)= 15. When t= 8 min, T(8)= Ta+ (To- Ta)e^(-8k)= 13.
    What do you get if you subtract e^(-8k)T(4)- e^(-4k)T(8)?

    You are asked to find T(0)= To.
  6. Jan 13, 2015 #5
    I got it! Thanks everyone for the help!
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