A vertical spring of force constant $100 {\mathrm{Nm}}^{-1}$ is attached to the ceiling, with a block of mass $10 \mathrm{kg}$ suspended from it. Now an external force $F$ is applied on the block so that the spring is stretched by an additional length of $2 \mathrm{m}$. The work done by the force $F$ is [Take $g=10 {\mathrm{ms}}^{-2}$]