I've got a homework question i'm stumped on.
The viscosity of the ethylene gas was measured at $99.8\times10^{-7}\ \mathrm{N\ s\ m^{-2}}$ at $288\ \mathrm K$. Calculate the collision diameter in $\overset{\circ}{\mathrm{A}}$ for this gas molecule.
I started with
$$\eta=\frac{m\overline v}{3\sqrt2\pi d^2} $$
then i said
$$\overline v=\sqrt{\frac{8RT}{\pi M}}$$
Molar mass $M=28.05\ \mathrm{g\ mol^{-1}}$
So my equation looks like
$$\eta=\frac{m}{3\sqrt2\pi d^2}\sqrt{\frac{8RT}{\pi M}} $$
but $m$ is still a variable. What should I do from here? Is there another substitution I can do?
So apparently my confusion about solving this problem, came from a lack of understanding what the $m$ variable was supposed to represent. I had thought that it was the total mass of the system, but it is actually the mass of one molecule.