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  4. A spherical ball is dropped in a long column of viscous liquid. Which of the following graphs represent the variation of (i)gravitational force with time (ii) viscous force with time (iii) net force acting on the ball with time? <img class=img-fluid question-image alt=Question src=https://cdn.tardigrade.in/q/nta/p-fxcsbbqemt6ktpst.jpg />

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Q. A spherical ball is dropped in a long column of viscous liquid. Which of the following graphs represent the variation of
(i)gravitational force with time
(ii) viscous force with time
(iii) net force acting on the ball with time?
Question

NTA AbhyasNTA Abhyas 2022

Solution:

Gravitational force remains constant on the falling spherical ball. It is represented by straight line $P$ . The viscous force $\left(\right.F=6\pi \etarv\left.\right)$ 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 $R$