Question

An 8 kg mass is supported by an aluminum wire of length 80 cm abd diameter 2.0mm. How much will the wire stretch?

Answer 1

First find from the book or Internet the Young's modulus (E) for aluminium.
I use E=69 GPa for aluminium.

Using stress = force (mg) / cross sectional area

ε=Strain = extension/unit length
= stress/E

stretching = extension
=ε * length
=stress*length/E

you can take it from here.