A spherical ball of radius $3.0\times {10}^{–4} \mathrm{m}$ and density ${10}^4 \mathrm{kg} {\mathrm{m}}^{-3}$ falls freely under gravity through a distance $h$ before entering a tank of water. If after entering the water the velocity of the ball does not change, find $h$. Viscosity of water is $9.8\times {10}^{–6} \mathrm{N} \mathrm{s} {\mathrm{m}}^{-2}$. $[g= 9.8 \mathrm{m} {\mathrm{s}}^{-2}, {\rho }_w=1000 \mathrm{kg} {\mathrm{m}}^{-3}]$

An oil drop falls through the air with a terminal velocity of $5 \times {10}^{–4} \mathrm{m} {\mathrm{s}}^{-1}$. The radius of the drop will be: $\eta =3.6\times {10}^{-5 }\mathrm{N} \mathrm{s} {\mathrm{m}}^{-2}, {\mathrm{\rho }}_{\mathrm{oil}}=900 \mathrm{kg} {\mathrm{m}}^{-3}$.,$g=10 \mathrm{m} {\mathrm{s}}^{-2}$

Neglect the density of air as compared to oil.

A spherical ball is dropped in a long column of viscous liquid. Which of the following graphs represent the variation of

(i) gravitational force with time.

(ii) viscous force with time.

(iii) net force acting on the ball with time.