143. Solving a chemistry problem

3.11. The boundary between the gold hydrosol and the dispersion medium in the centrifugal field of the ultracentrifuge 1 hour after the start of the experiment was at a distance of 3.70 cm from the axis of rotation, and after 1.5 hours at a distance of 3.78 cm. Determine the size and specific surface (calculated per unit mass) of spherical particles of a hydrosol, if the rotational speed of the centrifuge rotor is 8700 rpm,
the density of gold is 19.3 g / cm3, the density of water is 1 g / cm3, the viscosity of water is 1 * 10–3 Pa * s.