Extracted text: A steel rod of length L and uniform cross sectional area A is secured between two walls, as shown. Use L=1.7 m, E = 200 GPa, a = 11.9 x 10-8 /°C and AT = 70 °C. Calculate the stress for a temperature increase of AT for: a) The walls are fixed. b) The walls move apart a distance 0.4 mm. L