Asimply supported wood beam of rectangular cross section and span length 1.2 m carries a concentrated load p at midspan in addition to its own weight (see gure). the cross section has width 140 mm and height 240 mm. the weight density of the wood is 5.4 kn/m3 . 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.