# Homework Help: Thermo: Newtons law of cooling for radiation

1. Oct 21, 2011

### armolinasf

1. The problem statement, all variables and given/known data

A cube of copper of mass 4 kg and initial temperature of 110 oC is set to radiatively cool in an environment of 100 oC.
(Note: copper has an emissivity of about 0.05. Also, neglect conduction and convection as cooling agents in this problem.)

The surface area of the cube is .035 m^2

3. The attempt at a solution

Before the copper has had a chance to cool, find the net rate of heat transfer of the cube to the environment.

Using Pnet=Aes(to^4-ts^4), s=stefan boltzman constant, to= temp of object, ts= temp of surroundings, e=emissivity, a= surface area

(.035)(.05)(5.67*10^-8)(383.15^4-373.15^4)=.215 W

Is this correct?

The next part of the question asks for Newton's cooling approximation, which approximation is this I wasn't able to find a formula for it...

Thanks, and as always help is much appreciated!

2. Oct 21, 2011

### ehild

3. Oct 21, 2011