4. A shaft with a length L = 2.0 m is subjected to torques T = 5.10 kNm at either end. (See Fig. Q4). Segment AB (L = 1.0 m) is made of brass (Gb = 41.3 GPa) and has a square cross section (a = 75 mm). Segment BC (L2 = 1.0 m) is made of steel (Gs = 74.3 GPa) and has a circular cross section (d = 75 mm). Ignore stress concentrations near B. (a) Find the maximum shear stress and angle of twist for each segment of the shaft. (b) Find a new value for the dimension a of bar AB, if the maximum shear stress in AB and BC are to be equal. (c) Repeat part (b) if the angles of twist of segments AB and BC are to be equal. (d) If dimension a is reset to a = 75 mm and bar BC is now a hollow pipe with an outer diameter d = a, find the inner diameter d such that the angles of twist of segments AB and BC are equal. (Ex. 3-13 of Goodno & Gere, 9e, units changed to SI) A a B T a Gb, L1 Gs, L Fig. Q4