Terminal Speed in Projectile Motion under Air Resistance

[th4450]

Homework Statement

Terminal speed = 43 m s^-1

Homework Equations

Acceleration in y direction when ball falling down: a_y = - g + $\alpha$vv_y
where $\alpha$ = K/m
and v = (v_x² + v_y²)^0.5

The Attempt at a Solution

Putting a_y = 0 as there is no acceleration when terminal speed occurs.
However, is vv_y equal to v², i.e. 43² here?
Or do I have to compute its velocity in the y direction?

 

[haruspex]

When at terminal speed (near as dammit), what can you say about the horizontal component?