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 $\displaystyle F = -k_{1}v$;

(b) Force proportional to the square of speed so that $\displaystyle F = -k_{2}v^{2}$.

Investigate the dependence of $\displaystyle k_1$ on $\displaystyle \mu $, the viscosity of air and $\displaystyle r $, the effective radius of the body.Show that model (b) assumes that $\displaystyle k_2$ is independent of the viscosity of air.

The bit in bold is the part I can't do - I got $\displaystyle k_1 \propto \mu r $ for the first bit. Thanks very much and any help is appreciated.