question: A high carbon steel wire, circular in cross section, has a diameter of 0.1mm. what is the force needed to break it? ( the ultimate tensile stress of high carbon steel is 1.0 x 10(9) Pa).



Heres my attempt:

Stress = Force / cross-sectional area.

guess what? we are missing the cross sectional area.

So, diameter is 0.1mm, so radius must be 0.05mm. Area of a circle = r2 x pie

0.05(2) x 3.14 = 7.0 x 10(-3) --- here is our cross-sectional area.

So now we have 1.0 x 10(9) = Force / 7.0 x 10(-3)
Force = 1.0 x 10(9) x 7.0 x 10(-3)
Force = 7,000,000.......lolol.

^^WRONG^^

Please help :-)

you want your cross sectional area to be in m^2, not mm^2