Hello everybody, I am having trouble with this question:

Two common models for the resistive force experienced by a projectile in flight due to air resistance are:-

(a) Force proportional to speed so that ;

(b) Force proportional to the square of speed so that .

Investigate the dependence of on , the viscosity of air and , the effective radius of the body.Show that model (b) assumes that is independent of the viscosity of air.

The bit in bold is the part I can't do - I got for the first bit. Thanks very much and any help is appreciated.