Question

what is the force required for a steel wire to double it length when it's area cross-section is 1 square cm and Young modulus is 200GPa as the length of the wire is double the change in length is equal to the original length.

Answer 1

Determine strain:

$$\epsilon=\frac{\Delta L}L=\frac{\sigma}E=1,\\\space\\ \sigma=\frac FA,\\\space\\ F=\sigma A=EA=20·10^6\text{ N}.$$