You throw a rock horizontally off a cliff with a speed of 20 m/s. after two seconds, the magnitude of the velocity of the rock is closest to

So the magnitude of the resultant vector of the vertical and horizontal together is a right triangle with 20 on one side and 19.62 going down.

A^2 + B^2 = C^2

20^2 + 19.62^2 = C^2

400 + 385 = C^2

C = 28.0 m/s magnitude