A particle of mass 100 g is projected at time $\mathrm{t}=0$ with a speed $20 \mathrm{~ms}^{-1}$ at an angle $45^{\circ}$ to the horizontal as given in the figure. The magnitude of the angular momentum of the particle about the starting point at time $t=2 \mathrm{~s}$ is found to be $\sqrt{\mathrm{K}} \mathrm{kgm}^2 / \mathrm{s}$. The value of $K$ is $\_\_\_\_$ . (Take $\mathrm{g}=10 \mathrm{~ms}^{-2}$ )