A wire of length /and cross-sectional area A is made of a material of Young's modulus Y. If the wire is stretched by an amount x, the work done is
YAx22L
YAX2L2
YAx2L
Y=FLAl or F=YAlLdW=Fdl=YALldl∴ W=∫0x YALldl=YALl220X=YAx22L