The combination of a steel wire (length 80 cm , area of cross...

The combination of a steel wire (length 80 cm , area of cross section $1 \mathrm{~mm}^2$ ) and an aluminium wire (length 60 cm , area of cross section $3 \mathrm{~mm}^2$ ) joined end to end is stretched by a tension of 160 N . If the densities of steel and aluminium are $7.8 \mathrm{~g} / \mathrm{cc}$ and $2.6 \mathrm{~g} / \mathrm{cc}$ respectively then, the minimum frequency of a tuning fork which can produce standing waves in the composite wire, with the joint as a node, is