The area of cross-section of a railway track is 0 . 01 m ^ 2 . The...

Elastic energy $= \dfrac{Y}{2} ( strain{)}^{2} \times$ Area $\times$ length

$⇒$ Elastic energy per unit length $= \dfrac{Y}{2} ( strain{)}^{2} \times$ Area

$($strain $= \dfrac{\Deltaℓ}{ℓ} = \alpha\DeltaT = {10}^{- 5} \times 10 = {10}^{- 4} )$
$= \dfrac{{10}^{11}}{2} \times {\left({10}^{- 4}\right)}^{2} \times {10}^{- 2} = 5J{m}^{- 1}$