Physics · Strength of Materials

A steel bar is placed between two copper bars, each having the same area and length as the steel bar at 20°C. At this stage, they are rigidly connected together at both ends. When the temperature is raised to 320°C, the length of the composite bar increases by 1.5 mm. Determine the original length of the bar. (Take Es = 220 GN/m2, Ec = 110 GN/m2; αs = 1.2 × 10-5 /°C; αc = 1.75 × 10-5 /°C.)