Breaking stress for steel is $4\times {\text{10}}^6{\text{\hspace{0.17em}N/m}}^{\text{2}}$. The density of steel is $\text{8}\times {\text{10}}^3{\text{\hspace{0.17em}kg/m}}^{\text{3}}$ and $g=10m/s^2$. The maximum length of steel wire which will hang without breaking under its load is