A string of area of cross-section $4 \mathrm{~mm}^{2}$ and length $0.5 \mathrm{~m}$ is connected with a rigid body of mass $2 \mathrm{~kg}$. The body is rotated in a vertical circular path of radius $0.5 \mathrm{~m}$. The body acquires a speed of $5 \mathrm{~m} / \mathrm{s}$ at the bottom of the circular path. Strain produced in the string when the body is at the bottom of the circle is $\underline{\hspace{2cm}}$$\times 10^{-5}$. (use Young's modulus $10^{11} \mathrm{~N} / \mathrm{m}^{2}$ and $\mathrm{g}=10 \mathrm{~m} / \mathrm{s}^{2}$)