7. A 250 mm long steel bar has a round cross-section and a 5 mm diameter. The steel is alloy 4140 in the normalized condition (see Tables section for mechanical

properties). A 250 mm long aluminum bar with a round cross-section is also available. The aluminum alloy is Al 7075-T6 (also in Tables). (a) If both bars must have the same elastic deformation, how much heavier or lighter will the aluminum be than the steel in order to support a 40 kg load in pure tension? (Express your answer as a percentage of the weight difference between the two bars – for example: "the Al bar will be 16.2% lighter than the steel bar...") (b) If both bars must support the same maximum load in pure tension without permanent deformation,how much heavier or lighter will the aluminum be than the steel? (c) If both bars must support the same maximum load in pure tension without breaking, how much heavier or lighter will the aluminum be than the steel?