A string A of length 0.314 m and Young's modulus 2 × 10^10 N / m^2 is connected to another string B of length and Young's modulus both twice of those…

A string $\displaystyle A$ of length $\displaystyle 0.314$ m and Young's modulus $\displaystyle 2 \times 10^{10} \mathrm{~N} / \mathrm{m}^2$ is connected to another string $\displaystyle B$ of length and Young's modulus both twice of those of $\displaystyle A$. This series combination of strings is then suspended from a rigid support and its free end is fixed to a load of mass $\displaystyle 0.8$ kg . The net change in length of the combination is $\displaystyle \_\_\_\_$ mm. (radius of both the strings is $\displaystyle 0.2$ mm and acceleration due to gravity $\displaystyle =10 \mathrm{~m} / \mathrm{s}^2$ ) (Mass of both strings is to be neglected as compared to the mass of load)