a simply supported beam has a length of 1.2 m. the cross section has a width of 140 mm and height of 240 mm. the weight density of the beam 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.