What is the work function of metal if the light of wavelength 4000A^o generates photoelectron of velocity 6 x 10⁵ ms^-1 from it?

$$\begin{gathered} \mathrm{hv}={\mathrm{hv}}_0+\frac{1}{2}{\mathrm{mu}}^2=\mathrm{W}+\frac{1}{2}{\mathrm{mu}}^2 \\ \begin{array}{l}\therefore \mathrm{W}=\mathrm{hv}-\frac{1}{2}{\mathrm{mu}}^2\\ =\frac{6.626\times {10}^{-34}\times 3\times {10}^8}{4000\times {10}^{-10}}-\frac{1}{2}\times 9\times {10}^{-31}\times {\left(6\times {10}^5\right)}^2\\ =4.97\times {10}^{-19}-1.62\times {10}^{-19}\\ =3.35\times {10}^{-19}\mathrm{J}=\frac{3.35\times {10}^{-19}}{1.6\times {10}^{-19}}\mathrm{eV}=2.1\mathrm{eV}\end{array} \end{gathered}$$