A  certain  metal when irradiated  by light $\left(\mathrm{v}=3.2\times {10}^{16}\mathrm{Hz}\right)$ emits  photoelectrons  with  twice of K.E as did photoelectrons  when  the same  metal is irradiated  by light $\left(\mathrm{v}=2.0\times {10}^{16}\mathrm{Hz}\right)$. The ${\mathrm{v}}_0$ of the  metal is