# Thermal Stress Problem- not sure how to attack this one

## Homework Statement

The equation $F/A = -Y\alpha\Delta T$ gives the stress required to keep the length of a rod constant as its temperature changes. Show that if the length is permitted to change by an amount $\Delta L$ when its temperature changes by $\Delta T$, the stress is equal to $F/A = Y(\Delta L/L_0 - \alpha\Delta T)$.

## Homework Equations

thermal stress:
$F/A = -Y\alpha\Delta T$

solution:
$F/A = Y(\Delta L/L_0 - \alpha\Delta T)$

change in length:
$\Delta L = \alpha L_0\Delta T$

## The Attempt at a Solution

I figure this will have something to do with the area, as that's the only relation to the length I can see in the problem. I tried substituting A0 + deltaA in for A in the thermal stress equation, but that didn't seem to get me anywhere. Would really appreciate some direction with this one.