Q 11-09-008NEETNEET 2021Top questionMedium
The velocity of a small ball of mass M and density d, when dropped in a container filled with glycerine becomes constant after some time. If the density of glycerine is $\dfrac{d}{2}$, then the viscous force acting on the ball will be :
Answer: (B) $\dfrac{Mg}{2}$
At terminal velocity the net force is zero: weight $=$ buoyancy $+$ viscous force.
Volume of ball $= \dfrac{M}{d}$, so buoyancy $= \dfrac{M}{d}\cdot\dfrac{d}{2}\cdot g = \dfrac{Mg}{2}$.
$$F_v = Mg - \frac{Mg}{2} = \frac{Mg}{2}$$
Solution by Sreeraj P, M.Sc Physics