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Question

Which one of the following graphs represents the velocity-time ($v-t$) graph of a small spherical body falling in a viscous liquid?

This question was previously asked in
WBJEE 2026 Physics and Chemistry Question Paper (24-May-2026)
The correct answer is

To determine the correct velocity-time graph representing a small spherical body falling in a viscous liquid, we need to understand the physics of the scenario.

  1. The body experiences two main forces: gravitational force pulling it downwards and a viscous drag force opposing its motion.
  2. Initially, when the body starts falling, the gravitational force is dominant, and the velocity of the body increases.
  3. As the velocity increases, the viscous drag force also increases, which acts opposite to the gravitational force. This results in a net force that gradually decreases.
  4. Eventually, the body reaches a terminal velocity where the gravitational force equals the viscous drag force. At this point, the net force is zero, and thus the acceleration is zero.
  5. When the body reaches terminal velocity, it falls with a constant velocity.

From the above reasoning, the velocity-time graph should depict an initial increase in velocity followed by a constant velocity after some time.

The correct graph is the first option, where the velocity initially increases and then becomes constant, indicating the body has reached terminal velocity.

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