(2-6)  We can see that the distance travelled by the fish from where Nefertiti releases it to its impact on you is y and let’s say that time t passes while the fish is in motion. Meanwhile, during this same time t, Cormorant will have flown a distance x in the perpendicular direction.

①  velocity  =  distance/time  =  y/t

②  Using Pythagoras’ theorem, the distance moved by the fish relative to Cormorant = √(x2 + y2).    

 Therefore the velocity of the fish in Cormorant’s frame of reference  =  √(x2 + y2) / t.

Clearly this is greater than y/t, so the fish is moving faster as Cormorant sees it, than as Nefertiti does.