A string of area of cross-section $4 {\mathrm{mm}}^2$ and length $0.5$ 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 $5 \mathrm{m} {\mathrm{s}}^{-1}$ at the bottom of the circular path. Strain produced in the string when the body is at the bottom of the circle is _____ $\times {10}^{-5}$. (Use Young's modulus ${10}^{11} \mathrm{N} {\mathrm{m}}^{-2}$ and $g=10 \mathrm{m} {\mathrm{s}}^{-2}$)

Hence, the correct answer is 30.