JEE MAIN - Physics (2020 - 5th September Evening Slot - No. 2)
In an experiment to verify Stokes law, a small
spherical ball of radius r and density $$\rho $$ falls
under gravity through a distance h in air before
entering a tank of water. If the terminal velocity
of the ball inside water is same as its velocity
just before entering the water surface, then the
value of h is proportional to :
(ignore viscosity of air)
(ignore viscosity of air)
r
r4
r3
r2
Explanation
_5th_September_Evening_Slot_en_2_1.png)
After falling through h, the velocity be equal to terminal velocity
$$\sqrt {2gh} $$ = $${2 \over 9}{{{r^2}g} \over \eta }\left( {{\rho _l} - \rho } \right)$$
$$ \Rightarrow $$ h = $${2 \over {81}}{{{r^4}g{{\left( {{\rho _l} - \rho } \right)}^2}} \over {{\eta ^2}}}$$
$$ \Rightarrow $$ h $$ \propto $$ r4
Comments (0)
