Q.

A solid steel ball of diameter 3.6 mm acquired terminal velocity 2.45×102 m/s while falling under gravity through an oil of density 925 kg m3. Take density of steel as 7825 kg m3 and g as 9.8 m/s2. The viscosity of the oil in SI unit is          [2025]

1 2.18  
2 2.38  
3 1.68  
4 1.99  

Ans.

(4)

vT  29(ρ0ρl)r2gη

η=29(78259252.45×102)×(1.8)2×106×9.8

η=1.99