Discussion Forum

Consider two solid spheres P and Q each of density 8 gm cm^-3 and diameters 1 cm and 0.5 cm, respectively. Sphere P is dropped into a liquid of density 0.8 gm cm^-3 and viscosity η = 3 poiseulles. Sphere Q is dropped into a liquid of density 1.6 gm cm^-3 and viscosity η = 2 poiseulles. The ratio of the terminal velocities of P and Q is

Answer:

Explanation:

Terminal velocity is given by 

$v_{T}=\frac{2}{9}\frac{r^{2}}{\eta}(d-\rho)g$

$v_{T}=\frac{2}{9}\frac{r^{2}}{\eta}(d-\rho)g$

$\left(\frac{1}{0.5}\right)^{2}\times \left(\frac{2}{3}\right)\times \frac{(8-.08)}{(8-1.6)}=4\times \frac{2}{3}\times \frac{7.2}{6.4}=3$