Figure shows an observer $O_1$  floating on still water with ears in air. Another observer  $O_2$  in water moves towards surface with constant velocity  $v_1=\frac{v}{5}$. A source S emitting waves of freequency f moves towards $O_1$  with constant velocity  $v_s=\frac{v}{5}$. The velocity of sound in air is “ $v$” and velocity of  sound in water is “4v” (Assume doppler effect formulas are valid)