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) $\dfrac{Mg}{2}$
Concept. At terminal velocity, weight $=$ buoyancy $+$ viscous force.
Step 1. Buoyancy. Volume $\dfrac{M}{d}$, liquid density $\dfrac{d}{2}$: $F_B = \dfrac{Mg}{2}$.
Step 2. Viscous force. $F_v = Mg - \dfrac{Mg}{2} = \dfrac{Mg}{2}$.
Answer. $\dfrac{Mg}{2}$ (Option B).
Solution by Sreeraj P, M.Sc Physics