In Problem 236, how should the lengths of the two identical copper rods be changed so that each material will be stressed to its allowable limit?
A rigid block of mass M is supported by three symmetrically spaced rods as shown in Fig. P-236. Each copper rod has an area of 900 mm2; E = 120 GPa; and the allowable stress is 70 MPa. The steel rod has an area of 1200 mm2; E = 200 GPa; and the allowable stress is 140 MPa. Determine the largest mass M which can be supported.