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Need help on this question on Newtons law of cooling

by dan4loriel
Tags: cooling, newtons
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dan4loriel
#1
Apr30-12, 05:30 AM
P: 8
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 70C to 50C in 6mins when the temp of the surrounding is 30C. what wil be the tempt of the body after another 12mins if the cooling obeys newtons law of cooling


equation:
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=mc(70-50)

=20mc

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

dq=mc(50-θs)
dq-dt=mc(50-θs)/12=-k

got lost from here please help!!!!!
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sweet springs
#2
Apr30-12, 08:20 AM
P: 449
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.

regards.
dan4loriel
#3
Apr30-12, 09:03 AM
P: 8
thanks for the help

dan4loriel
#4
Apr30-12, 11:52 AM
P: 8
Need help on this question on Newtons law of cooling

hey,

wouldnt mind if you help me in solving them as regards to the equation given
berkeman
#5
Apr30-12, 11:58 AM
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P: 41,098
Quote Quote by dan4loriel View Post
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 70C to 50C in 6mins when the temp of the surrounding is 30C. what wil be the tempt of the body after another 12mins if the cooling obeys newtons law of cooling


equation:
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=mc(70-50)

=20mc

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

dq=mc(50-θs)
dq-dt=mc(50-θs)/12=-k

got lost from here please help!!!!!
Quote Quote by dan4loriel View Post
hey,

wouldnt mind if you help me in solving them as regards to the equation given
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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