$(A)$ $u=0.8 v$ and $f_5=f_0$
$(B)$ $u=0.8 v$ and $f_5=2 f_0$
$(C)$ $u=0.8 v$ and $f_5=0.5 f_0$
$(D)$ $u=0.5 v$ and $f_5=1.5 f_0$
$Y = A\sin (100t)\cos (0.01x)$
where $Y$ and $A$ are in millimetre, $t$ is in seconds and $x$ is in metre. The velocity of wave is ..... $m/s$