#drag force

PHYSICS

A sphere of radius 0.025 m moves at 0.08 m/s through blood ( eta = 2.7 × 10⁻³ Pa s ). What is the viscous drag force

Given: A sphere of radius 0.025 m moves at 0.08 m/s through blood ( eta = 2.7 × 10⁻³ Pa s ). What is the viscous drag force? These values define the system as per NCERT data. Formula: Stokes’ law: F = 6 π eta a v. This is the standard NCERT relation for this phenomenon. Substitution & Calculation: eta = 2.7 × 10⁻³ Pa s, a = 0.025 m, v = 0.08 m/s . F = 6 × 3.14 × 2.7 × 10⁻³ × 0.025 × 0.08 = 1.017 × 10⁻⁴ N . Result: The computed value matches the expected outcome and confirms the correct choice. Units and powers like J kg⁻¹ K⁻¹, m/s², 10⁻⁵ are properly used as per NCERT.

Ref: NCERT Physics Textbook for Class XI and XII, Chapter: Laws of Motion, Work Energy Power, Gravitation and System of Particles, Topic: Newton's laws, work-energy theorem and rotational dynamics.

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Equation of Continuity and Flow Rate

Which of the following statements is correct about terminal velocity?

Terminal velocity occurs when the viscous force (proportional to velocity) equals the net gravitational force, resulting in zero acceleration and constant speed, as per Stokes’ law. As per NCERT, applying relevant law/formula with correct units and sign convention leads to It occurs when forces balance. This satisfies dimensional consistency and physical conditions given, so option B is scientifically correct.

Ref: NCERT Class 11 Physics, Thermal Properties and Gravitation.

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Fluid Pressure, Pascal's Law and Manometers

What is the primary reason a heavy object falls faster than a lighter one through a viscous fluid?

Terminal velocity (v∝(mg−Fb)/6πηa) depends on weight minus buoyant force. A heavier object has a greater net downward force, increasing its terminal velocity compared to a lighter object of the same size.

Ref: NCERT Class 11 Physics, Thermal Properties and Gravitation.

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Fluid Pressure, Pascal's Law and Manometers

A sphere of radius 0.03m falls through machine oil (η\=0.113Pa s) at 0.15m/s. What is the viscous drag force?

Stokes’ law: F = 6πηav. η = 0.113Pa s, a = 0.03m, v = 0.15m/s. F = 6×3.14×0.113×0.03×0.15 = 0.0958N. As per NCERT, applying relevant law/formula with correct units and sign convention leads to 0.096 N. This satisfies dimensional consistency and physical conditions given, so option C is scientifically correct.

Ref: NCERT Class 11 Physics, Thermal Properties and Gravitation.

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Surface Tension, Capillarity and Excess Pressure

A plate of area 0.09m2 moves at 0.5m/s over a 1.0mm thick water film (η\=1.0×10−3Pa s). What force is required?

Viscous force: F = ηvAl. η = 1.0×10−3Pa s, v = 0.5m/s, A = 0.09m2, l = 1.0×10−3m. F = 1.0×10−3×0.5×0.091.0×10−3 = 1.0×10−3×45 = 0.045N. As per NCERT, applying relevant law/formula with correct units and sign convention leads to 0.045 N. This satisfies dimensional consistency and physical conditions given, so option B is scientifically correct.

Ref: NCERT Class 11 Physics, Thermal Properties and Gravitation.

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