# Homework Help: A challenge for professionals

1. Nov 25, 2008

### eduardalcazar

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

metal rod 30cm long expands by 0.075cm when its temp. is raised from 0C to 100C. A rod of diff. metal of the same length expands by 0.045cm for the same rise in temp. A third rod, also 30cm long is made up of pices of each of the above metals placed end-to-end expands 0.065cm between 0C to 100C.

What is the length of EACH composite bar.

3. The attempt at a solution

deltaL=initial L x coefficient of thermal expansion.

That formula was the similar from some of my friends. I tried it but still i found it out complicated. Thanks in advance to those who helped. God bless

2. Nov 25, 2008

### mgb_phys

The coefficient of thermal expansion is what fraction of it's original length a material expands for each 1deg change in temperature.
You can find this value for materials A and B from the numbers you are given.

Your equation isn't quiet correct, it should be: deltaL=initial L x coefficient of thermal expansion x CHANGE IN TEMPERATURE

3. Nov 25, 2008

### eduardalcazar

please state your help in equation with explanations. I was able to find the answer but not sure. in my computation the answer 20. I just need a justification in this answer.

Thanks..

4. Nov 25, 2008

### mgb_phys

This site is to teach people how to answer science questions and help them when they go wrong - we don't just supply answers.
I suggest you post your calculations of the coeff for the two materials.
Then we will explain how to do part 2.