Using dimensional analysis, angular frequency $\left(\omega \right)$ of surface waves in a lake as a function of surface tension $\sigma$, water density Q and the wave number $k=\frac{2\pi }{\lambda }$ 
($\lambda$  is the wavelength) is derived. Assuming the dimensionless coefficient is equal to two (in SI units) in this case, find the value of group velocity $\left(v_g\right)$  where  $v_g=\frac{\partial \omega }{\partial k}.$ If your answer is $v_g$ (in m/s) then fill value of $10v_g$

$(Use:\sigma =64mN.m^{-1},Q=320\pi kg{m}^{-3},\lambda =1cm)$