Assertion: When an ideal fluid flows through a horizontal...

Assertion: When an ideal fluid flows through a horizontal tube of variable cross-section, the pressure becomes different at different points. Reason: Raindrops falling from a great height reach the ground with a relatively small velocity. This phenomenon involves the viscosity of air. (A) $\mathrm{A}$ (B) $\mathrm{B}$ (C) $\mathrm{C}$ (D) D

Assertion: When an ideal fluid flows through a horizontal tube of variable cross-section, the pressure becomes different at different points. Reason: Raindrops falling from a great height reach the ground with a relatively small velocity. This phenomenon involves the viscosity of air.
(A) $\mathrm{A}$
(B) $\mathrm{B}$
(C) $\mathrm{C}$
(D) D

Key Concepts

Terminal Velocity

Terminal velocity is the constant speed attained by a falling object when the viscous drag force exerted by the fluid balances the gravitational force. This concept is key in explaining why raindrops, despite falling from a great height, do not continuously accelerate but instead reach a relatively small, steady velocity.

Bernoulli's Principle

This principle governs the behavior of an ideal fluid in motion, stating that along a streamline, the sum of the pressure energy, kinetic energy, and potential energy per unit volume remains constant. It explains why pressure varies in a tube of varying cross-section as the fluid speed adjusts to conserve energy.

Continuity Equation

The continuity equation for fluid flow asserts that for an incompressible fluid, the mass flow rate remains constant throughout its motion. This implies that in a tube with varying cross-sectional area, the velocity of the fluid must change to maintain a constant flow, which in turn affects the pressure distribution.

Viscosity

Viscosity is a measure of a fluid's resistance to deformation and shear stress. In the context of fluid dynamics, it is the property that distinguishes ideal (inviscid) fluids from real fluids, contributing to effects such as drag and energy dissipation. Viscosity is crucial for understanding phenomena where frictional forces play a significant role, like air resistance.

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