A bar, L metre long and having its area of crosssection A, is subjected to gradually applied tensile load W. The strain energy stored in the bar is given by

A

$$\frac{W^2L}{AE}$$

B

$$\frac{W^2L}{2AE}$$

C

$$\frac{WL}{2AE}$$

D

$$\frac{WL}{AE}$$