Question

A spherical ball of iron of radius $2 \,mm$ is falling through a column of glycerine. If densities of glycerine and iron are respectively $1.3 \times 10^{3} \,kg / m ^{3}$ and $8 \times 10^{3} \,kg / m ^{3} \cdot \eta$ for glycerine $=0.83 \, Nm ^{-2} \sec$, then the terminal velocity is

• A. 0.7 m / s
• B. 0.07 m / s
• C. 0.007 m / s
• D. 0.0007 m / s

Answer 1

Answer: (B)

Terminal velocity, $v_{0}=\frac{2 r^{2}\left(\rho-\rho_{0}\right) g}{9 \eta}$
$=\frac{2 \times\left(2 \times 10^{-3}\right)^{2} \times(8-1.3) \times 10^{3} \times 9.8}{9 \times 0.83}$
$=0.07\, ms ^{-1}$