Q.

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 d2, then the viscous force acting on the ball will be             [2021]
 

1 2Mg  
2 Mg2  
3 Mg  
4 32Mg  

Ans.

(2)

Given, Mass of ball = M

Density of ball = d

Density of given wire = d2

Viscous force = weight - buoyant force 

=vdg-v(d2)g

=vdg(1-12)=vdg2                            ...(i)

Also mass, M=vd

So, from equation (i), 

Viscous force=Mg2