Atimber beam ab of length l and rectangular cross section car- ries a single concentrated load p at its midpoint c.

(a) show that the ratio tm/sm of the maximum values of the shearing and nor- mal stresses in the beam is equal to h/2l, where h and l are, respectively, the depth and the length of the beam.

(b) determine the depth h and the width b of the beam, knowing that l 5 2 m, p 5 40 kn, tm 5 960 kpa, and sm 5 12 mpa.