Q.

A small ball of mass m and density ρ is dropped in a viscous liquid of density ρ0. After some time, the ball falls with constant velocity. The viscous force on the ball is:   [2024]

1 mg(ρ0ρ-1)  
2 mg(1-ρρ0)  
3 mg(1-ρρ0)  
4 mg(1-ρ0ρ)  

Ans.

(4)

At constant velocity, Fv+FB=mg

FB=ρ0·(mρ)·g

Fv=mg-FB=mg-mρρ0gFv=mg(1-ρ0ρ)