Question

If the terminal speed of a sphere of material A (density = 9.5 kg/$m^3$) is $4m/s$ in a viscous liquid (density = 6.5 kg/$m^3$), find the terminal speed of a sphere of material B (density = 3.5 kg/$m^3$) of the same size in the same liquid. (The ball of B is released from bottom in a very deep container)

• A. 6.4 m/s
• B. 3 m/s
• C. 8 m/s
• D. 4 m/s

Answer 1

The correct option is D 4 m/s

$v=\frac{2}{9}\frac{r^2}{n}({\rho }_{solid}-{\rho }_{fluid})g$

in both case difference is same
when ${\rho }_s>{\rho }_f\to$ we get $V_{terminal}$ in downward direction.
when ${\rho }_s<{\rho }_f\to$ we get $V_{terminal}$ in upward direction.