The terminal velocity of a copper ball of radius `2mm` falling through a tank of oil at `20^(@)C` is `6.5cm//s`. Find the viscosity of the oil at `20^(@)C`. Density of oil is `1.5xx10^(3)Kg//m^(3)`, density of copper is `8.9xx10^(3)Kg//m^(3)`.

Explanation

We have `v_1=6.5 times 10^2 ms^-1,a=2 times 10^3m `
`g=9.8 ms^-2,p=8.9 times 10^3 kg m^-3`
`sigma=1.5 times 10^3 kg m^-3`. From Eq. (10.20)
`eta=2/9 times ((2 times 10^-3)^2 m^2 times 9.8 ms^-2)/(6.5 times 10^-2 ms^-1) times 7.4 times 10^3 kg m^-3`
`=9.9 times 10^-1 kg m^-1 s^-1`