# An Aluminium and Copper wire of same cross sectional area but having lengths in the ratio 2 : 3 are joined end to end. This composite wire is hung from a rigid support and a load is suspended from the free end. If the increase in length of the composite wire is 2.1 mm , the increase in lengths of Aluminium and Copper wires are : [$Y_{AI} = 20\times 10^{11}N/m^2\: and \: Y_{Cu} = 12 \times 10^{11} N/m^2]$

$\begin {array} {1 1} (1)\;0.7\: mm; 1.4\: mm & \quad (2)\;0.9\: mm;1.2\: mm \\ (3)\;1.0\: mm;1.1\: mm & \quad (4)\;0.6\: mm;1.5\: mm \end {array}$

(4) 0.6 mm ; 1.5 mm