# A vertical spring of force constant 100 N/m is attached with a hanging mass of 10 kg. Now an external force is applied on mass so that the spring is stretched (maximum) by additional 2 m. The work by the force F is (g=10m/s 2)

We know that work done is give by

$$\begin{array}{l}W=\frac{1}{2}kx^{2}\end{array}$$
$$\begin{array}{l}W=\frac{1}{2}100(2^{2})=200J\end{array}$$