A simply supported wood beam of rectangular cross section and span length 1.2 m carries a concentrated load Pat midspan in addition to its own weight (see figure). The cross section has width 140 mm and height 240 mm. The weight density of the wood is 5.4 kN/m. Calculate the maximum permissible value of the load P if (a) the allowable bending stress is 8.5 MPa, and (b) the allowable shear stress is 0.8 MPa. 240 mm 140 mm 0.6 m- -0.6 m-