A steel rod has a radius of 20 mm and a length of 2.0 m. A force of 62.8 kN stretches it along its length. Young’s modulus of steel is $2.0 \times 10^{11} \mathrm{~N} / \mathrm{m}^2$ The longitudinal strain produced in the wire is ______ × $10^{-5}$.
