Question

A spherical ball is dropped in a long column of viscous liquid. Which of the following graphs represent the variation of

(i) the gravitational force with time

(ii) the viscous force with time

(iii) the net force acting on the ball with time

• A. $Q,R,P$
• B. $R,Q,P$
• C. $P,Q,R$
• D. $R,P,Q$

Answer 1

Answer: (C)

Gravitational force remains constant on the falling spherical ball. It is represented by straight line $P$ . The viscous force $(F=6\pi \eta rv)$ increases as the velocity increases with time. Hence, it is represented by curve $Q$ .
Net force = gravitational force $-$ viscous force
As viscous force increases, net force decreases and finally becomes zero. Then the body falls with a constant terminal velocity. It is thus represented by curve $R$ .