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 $\rho$ and $\sigma$ respectively, and the viscosity of the liquid is $\eta$).
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 $\rho$ and $\sigma$ respectively, and the viscosity of the liquid is $\eta$).
- A
$\frac{{{r^2}g}}{{9\eta }}(\rho - 2\sigma )$
- B
$\frac{{{r^2}g}}{{9\eta }}(2\rho - \sigma )$
- C
$\frac{{{r^2}g}}{{9\eta }}(\rho - \sigma )$
- D
$\frac{{2{r^2}g}}{{9\eta }}(\rho - \sigma )$
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