A composite bar is 350 mm long and consists of a copper tube butt-welded to the end face of a steel bar. The tube dimensions are 30 mm diameter x 20 mm bore x 200 mm long, and the steel bar is 30 mm diameter and 150 mm long. If the bar supports an axial force of 4 kN, determine (a) The stresses in the copper and the steel. (b) The change in length of the composite bar. For steel, E = 200 GN/m? ; for copper, E = 120 GN/m?.