physics, engineering, youngs modulus?

Question

the end of a copper wire of diameter 0.30mm and length 1.50m is fused to one end of a steel wire of the same diameter and 1.20m in length. The wire is then hung vertically by attaching the free copper end to a fixed point and attaching a small weight to the lower end of the steel wire. The attachments reduce the length of each wire by 20mm. A load weight of 30N is then hung from the lower end of thesteel wire. Calculate
a) the stress in each wire,
b) the strain in each wire given that the Youngs modulas for steel is 2.0*10(power11)Nm(power-2) and for copper is 1.3*10(power11)Nm(power-2)
c) the total extension of the two wires

Answer 1

the stress is the same everywhere, load divided by area.

the strain will be different in each wire because the modulus of elasticity (Young's modulus) is different for Cu than for steel. If the stress is less than the yield strength, i.e., not enough to produce permanent deformation, then the strain is all elastic. You need the "gage' length of wire, i.e., how much of each wire experiences the stress. Then treat each wire as a spring, Hookes law. The spring constant is the modulus.

The total extension of the two wires is just the sum of the total stretch in Cu plus the total stretch in steel

Good luck