A wire suspended vertically from one of its ends is stretched by attaching a weight of $200\mathrm{N}$ to the lower end. The weight stretches the wire by $1\mathrm{m}\mathrm{m}$. Then the elastic energy stored in the wire -

A steel plate of face area $1{ \mathrm{cm}}^2$ and thickness $4 \mathrm{cm}$ is fixed rigidly at the lower surface. A tangential force $F=10 \mathrm{kN}$ is applied on the upper surface as shown in the figure. The lateral displacement $x$ of upper surface w.r.t. the lower surface is (Modulus of rigidity for steel is $8\times {10}^{11} \mathrm{N} {\mathrm{m}}^{-2}$ )

A vertically downward force $F$ is applied on a light wire of length $l$, cross-sectional area $A$ and Young's modulus $Y$ as shown in the figure. The extension in length of the rod will be