For a simply supported beam of length L, the bending moment M is described as M = a (x - x^{3}/L^{2}), 0 ≤ x < L; where a is a constant. The shear force will be zero at

If a rectangular beam measuring 10 x 18 x 400 cm carries a unformly distributed load such that the bending stress developed is 100 kg/cm^{2}. The intensity of the load per metre length, is