If Aluminum and steel are connected as one rod, and are attached to the wall and is pulled upon. How would the change in length for each material of the rod be calculated? I'm given that the Aluminum section is twice as long as the steel section, and the total change in length of the whole rod is 1mm. So far, i've said: F = Y(delta-L / L-naught)A + Y(delta-L / L-naught)A *Where, the first part is for Aluminum, and the Second part is for Steel. Manipulating this equation I got: (2Fx)/A = (6.9E10)(delta-Laluminum) + (4E11)(delta-Lsteel) and, delta-Aluminum + delta-steel = 0.001m *where x = the length of steel, therefore aluminum = 2x. This is where i'm stuck. I dont' know the Force applied, or the Area of the rod. What can i do? Thanks in advance for any help.