Consider a circular hollow section, with outer diameter d=155mm, and thickness t=3mm. The circular hollow section is mad

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Consider a circular hollow section, with outer diameter d=155mm, and thickness t=3mm. The circular hollow section is made from aluminium which has a density of 2700 kg/m and a shear modulus G = 30000 MPa. What twisting moment (in kNm) will cause a maximum shear stress of 105MPa?
Q2) The CHS has changed so thickness is now 1.5t but the diameter is unchanged. The material is changed to steel which has density = 7850kg/m^3 and shear modulus G = 70000MPa. What twisting moment (in kNm) will cause a maximum shear stress of 105MPa?
Q3) The CHS (the one from Q2) is now filled with concrete which has density = 2450kg/m^3. What is the mass per unit length of the concrete filled CHS (in kg/m)? Use g = 10m/s^2.