When an elastic material with Young's modulus Y is subjected to a stretching stress s, the elastic energy stored per unit volume of the material
Y s / 2
s2 Y/2
s2 / 2y
s / 2y
E = Energy stored per unit volume=12× stress × strain =12×s× strain Further. strain = stress Y=sY∴ E=12×s×sY=s22Y