Answer: About 60 MPa; an equivalent steel bar would be much thicker.
Step-by-step explanation:
The tensile strength (TS) of a material is the maximum stress it can withstand before failing under tension. It is usually measured in units of megapascals (MPa). The TS of a material depends on its composition and microstructure, as well as the testing conditions.
Given that a bar made of the aluminum alloy with a cross-section of 2 cm^2 can withstand pulling up to about 120000 N, we can calculate its tensile strength as follows:
TS = force / cross-sectional area = 120000 N / (2 cm)^2 = 30000 kPa = 30 MPa.
Therefore, the tensile strength of the aluminum alloy is about 30 MPa.
To compare with an equivalent steel bar of tensile strength 500 MPa, we need to calculate the cross-sectional area of the steel bar that can withstand the same force.
120000 N is the maximum force that the aluminum bar can withstand, so we want to find the cross-sectional area of the steel bar that can withstand 120000 N with a TS of 500 MPa:
TS = force / cross-sectional area
cross-sectional area = force / TS = 120000 N / 500 MPa = 0.24 cm^2.
Therefore, the steel bar needs to have a cross-sectional area of 0.24 cm^2 to withstand the same force as the aluminum bar. Since the steel bar has a higher tensile strength, it can be thinner than the aluminum bar.
The area of the aluminum bar is 2 cm^2, so the steel bar would be much thinner:
0.24 cm^2 / 2 cm^2 = 0.12.
Therefore, the equivalent steel bar would be much thinner than the aluminum bar. The correct answer is (C) about 60 MPa; an equivalent steel bar would be much thicker is incorrect.