7. At a temperature of 15°C, a gap of A-5 mm exists between the two polymer bars shown in the accompanying figure. Bar (1) has a length L₁ = 700 mm, a cross-sectional area A, 1,250 mm², a coefficient of thermal expansion a, = 130 x 10-6/°C, and an elastic modulus E. 1,400 MPa. Bar (2) has a length La=500 mm, a cross-sectional area A₁ = 3.750 mm², a coefficient of thermal expansion a, = 80 x 10-6/°C, and an elastic modulus E, 3,700 MPa. The supports at A and D are rigid. Determine (a) the lowest temperature at which the gap is closed. (b) the normal stress in the two bars at a temperature of 100°C. (c) the longitudinal normal strain in the two bars at 100°C. 12 (1) (2)