The terminal velocity of a copper ball of radius 2 mm falling through a tank of oil at `20^@C` is `6.5 cm s^(-1)`. Compute the viscosity of the oil at `20^@ C` . Density of oil `=1.5 xx 10^(3) kg m^(-3)` density of copper is `8.9 xx 10^(3) kg m^(-3)`.

Explanation

`eta = 2/9 (r^2)/v (rho - rho.) g = (2 xx (2 xx 10^(-3))^(2) xx (8.9 xx 10^3 - 1.5 xx 10^3) xx 9.8)/(9 xx 6.5 xx 10^(-2))`
`eta = 0.992` decapoise