Mechanical Properties Of Solids

If is the stress and is the Young?s modulus of material of a wire, the energy stored in the wire per unit volume is

Two wires of equal cross section, but one made up of steel and the other copper are joined end to end. When the combination is kept under tension, the elongations in the two wires are found to be equal. If (Y for steel = and , the ratio of the lengths of the two wires is