Spring Potential Energy

Q. A spring $40\text{mm}$ long is stretched by applying a force. If $10\text{N}$ force is required to stretch the spring through $1\text{mm}$, then work done in stretching the spring through $40\text{mm}$ is

1. $24\text{J}$
2. $8\text{J}$
3. $56\text{J}$
4. $64\text{J}$

Q. If a spring extends by $x$ on loading, then energy stored by the spring is (Given: $T$ is the tension in spring and $k$ is spring constant)

1. $\frac{T^2}{4k}$
2. $\frac{2T^2}{k}$
3. $\frac{T^2}{2k}$
4. $\frac{T^2}{k}$