Why are springs made of steel instead of copper?

$A$ steel rail of length $5\,m$ and area of cross-section $40\,cm^2$ is prevented from expanding along its length while the temperature rises by $10\,^{\circ}C$. If the coefficient of linear expansion and Young's modulus of steel are $1.2\times10^{-5}\,K^{-1}$ and $2\times10^{11}\,N/m^2$ respectively,the force developed in the rail is approximately:

Two wires are made of the same material and have the same volume. The first wire has cross-sectional area $A$ and the second wire has cross-sectional area $3A$. If the length of the first wire is increased by $\Delta l$ on applying a force $F$,how much force is needed to stretch the second wire by the same amount?

Two persons pull a wire towards themselves. Each person exerts a force of $200 \, N$ on the wire. Young's modulus of the material of the wire is $1 \times 10^{11} \, N \, m^{-2}$. The original length of the wire is $2 \, m$ and the area of cross-section is $2 \, cm^2$. The wire will extend in length by $...... \, \mu m$.

If $\delta$ is the depression produced in a beam of length $L$,breadth $b$ and thickness $d$,when a load $W$ is placed at the mid-point,then:

$A$ $4 \ kg$ stone attached at the end of a steel wire is being whirled at a constant speed $12 \ ms^{-1}$ in a horizontal circle. The wire is $4 \ m$ long with a diameter $2.0 \ mm$ and Young's modulus of the steel is $2 \times 10^{11} \ Nm^{-2}$. The strain in the wire is: