Velocity of wave at a distance $x$ from lower end is
$v_x=\sqrt{2 g x}$
Time $d t=\frac{d x}{\sqrt{2 g x}}$
Integrating for 0 to $L$ we get
$\sqrt{\frac{4 l}{g}}$
Which one of the following correctly shows the direction of the velocity of the points $1, 2$ and $3$ on the string
