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

1. Apr 30, 2012

### dan4loriel

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

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

2. Apr 30, 2012

### sweet springs

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.

3. Apr 30, 2012

### dan4loriel

thanks for the help

4. Apr 30, 2012

### dan4loriel

hey,

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

Last edited by a moderator: Apr 30, 2012
5. Apr 30, 2012

### 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.