Physics in senior high school: there is a parabolic small pool (the plane is parabolic)

h=gt^2/2

Let the parabolic equation be x 2 = 2ay.

Substitute h and l/2 to get a=l/8h.

When y=h/2, x= root 2l/4.

So the root sign 2l/4=vt.

V = 5m/s