The rails of a railroad track are welded together at their ends (to form continuous rails and thus eliminate the clacking sound of the wheels) when the temperature is 60°F.
What compressive stress σ is produced in the rails when they are heated by the sun to 120°F if the coefficient of thermal expansion α = 6.5 × 106 / °F and the modulus of elasticity E = 30 × 106 psi?