Problem $3.$ There is gap between the three copper bars and the rigid slab that is supported by two aluminum bars at $15C,=0\mathrm{.}20mm.$

For each copper bar, $A=500m{m}^2,E=120$GPa, and $a=16\mathrm{.}8\frac{m}{mC}.$ For the aluminum bars, $A=400m{m}^2,E=70$GPa, and $a=$

$23\mathrm{.}1\frac{m}{m*C}.$ Neglecting the mass of the slab and when the temperature in the assembly is increased to $60C,$

a$)$ Determine the stress in the aluminum.

b$)$ Determine the stress in the copper. Show the complete FBD:

For Problem $3$