What is the velocity v of a metallic ball of radius r falling in a tank of liquid at the instant when its acceleration is one-half that of a freely falling body ? (The densities of metal and of liquid are r and s respectively, and the viscosity of the liquid is `eta`).

Options

A. `(r ^(2) g )/( 9 eta) (rho -2 sigma)`
B. `( r ^(2)g )/(9 eta) ( 2 rho - sigma )`
C. `(r ^(2)g )/( 9 eta ) (rho - sigma)`
D. `(2 r ^(2)g)/(9 eta)(rho -sigma )`

Answer

C