The bar has a cross-sectional area $0.25 \text{ in}^2$, length $2 \text{ ft}$, modulus of elasticity $29 \cdot 10^3 \text{ kip/in}^2$, and coefficient thermal expansion $6.6 \cdot 10^{-6} /^\circ\text{F}$. It is constrained to just fit between the two fixed supports when $T_1 = 60 ^\circ\text{F}$. If the temperature is raised to $T_2 = 120 ^\circ\text{F}$, determine the average normal stress developed in the bar.