A round steel bar of overall length 20 cm consists of two equal portions of 10 cm each having diameter of 4 cm and 5 cm respectively if the rod is subjected to a tensile load of 10 tonnes then what will be the elongation (where modulus of elasticity E = 2 ×106 kg/cm2)?

• A. \(\frac{1}{{10\pi }}\left[ {\frac{1}{{25}} + \frac{1}{{16}}} \right]\)
• B. \(\frac{2}{{10\pi }}\left[ {\frac{1}{{25}} + \frac{1}{{16}}} \right]\)
• C. \(\frac{3}{{10\pi }}\left[ {\frac{1}{{25}} + \frac{1}{{16}}} \right]\)
• D. \(\frac{4}{{10\pi }}\left[ {\frac{1}{{25}} + \frac{1}{{16}}} \right]\)