When an elastic material with Youngs modulus Y is subjected to stretching stress S, elastic energy stored per unit volume of the material is
(a) YS/2
(b) S2Y/2
(c) S2/2Y
(d) S/2Y
When an elastic material with Youngs modulus Y is subjected to stretching stress S, elastic energy stored per unit volume of the material is
(a) YS/2
(b) S2Y/2
(c) S2/2Y
(d) S/2Y