Not sure how to go about solving this problem:
What outer diameter must a 2mm thick hollow rod have in order to have the same structural bending strength as a solid rod with diameter of 7mm? Also compare the weight per unit lenght of the two rods. Assume that material is stainless steel (E=180MPa) having weight density of 7.78 x 10^4N/m^3.
Does the 2mm thick refer to the lenght of the hollow rod? where does weight density play into the equation?
stress = Mc/I
Bending rigidity -> ymax= cFl^3/EI
Thank you in advance for any information you can provide.