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Homework Help: Need help on this question on Newtons law of cooling

  1. Apr 30, 2012 #1
    1. The problem statement, all variables and given/known data

    please i need help as have been trying to solve this question: A body cools from 70°C to 50°C in 6mins when the temp of the surrounding is 30°C. what wil be the tempt of the body after another 12mins if the cooling obeys newtons law of cooling

    dq/dt = -k(θ-θs)

    where m- mass of the body
    c-specific heat capacity of the body
    θ-temp of the body
    θs-temp of the surrounding or room

    3. The attempt at a solution

    i tried sovling it as follows:



    dq/dt= 20mc/6= -k(70-50) =-20k


    got lost from here please help!!!!!
  2. jcsd
  3. Apr 30, 2012 #2
    Hi. by relation q=cθ the equation is

    dθ/dt = -k/c (θ-θs) solving it
    θ = (θ0-θs) e^-k/c t + θs
    where θ0 is initial temperature of the body.

  4. Apr 30, 2012 #3
    thanks for the help
  5. Apr 30, 2012 #4

    wouldnt mind if you help me in solving them as regards to the equation given
    Last edited by a moderator: Apr 30, 2012
  6. Apr 30, 2012 #5


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    Staff: Mentor

    We don't solve your homework problems for you here at the PF. We can give hints, like the one you got above. Now it is your turn to do wht work in solving the problem.

    BTW -- I fixed up the "txt speak" abbreviation in your post. We do not allow txt speak abbreviations like "d" or "u" here. Please re-read the Rules link at the top of the page. Thanks.
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