二、試說明具遺傳變異較低之光合作用補償點及可塑性高之樹種競爭力強的原因。(25分)

2. A simple beam consists of a wood member that is reinforced by 0.25 in. thick steel plates on top and bottom, as shown in Fig-2. \( E_s=30 \times 10^6 \) psi and \( E_w=1.5 \times 10^6 \) psi, respectively. Calculate the maximum bending stresses \( \sigma_s \) in the steel plates and \( \sigma_w \) in the wood member due to the uniform load. (20%)