#viscous force

Fluid Pressure, Pascal's Law and Manometers

A plate of area 0.07m2 moves at 0.3m/s over a 0.5mm thick water film (η\=1.0×10−3Pa s). What force is required?

Viscous force: F = ηvAl. η = 1.0×10−3Pa s, v = 0.3m/s, A = 0.07m2, l = 0.5×10−3m. F = 1.0×10−3×0.3×0.070.5×10−3 = 1.0×10−3×42 = 0.042N. As per NCERT, applying relevant law/formula with correct units and sign convention leads to 0.042 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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Surface Tension, Capillarity and Excess Pressure

A sphere of radius 0.015m moves at 0.2m/s through water (η\=1.0×10−3Pa s). What is the viscous force?

Stokes’ law: F = 6πηav. η = 1.0×10−3Pa s, a = 0.015m, v = 0.2m/s. F = 6×3.14×1.0×10−3×0.015×0.2 = 5.652×10−5N. As per NCERT, applying relevant law/formula with correct units and sign convention leads to 5.65 × 10⁻⁵ 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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Viscosity, Stokes' Law and Reynolds Number

A plate of area 0.09m2 moves at 0.5m/s over a 0.6mm thick machine oil film (η\=0.113Pa s). What force is required?

Viscous force: F = ηvAl. η = 0.113Pa s, v = 0.5m/s, A = 0.09m2, l = 0.6×10−3m. F = 0.113×0.5×0.090.6×10−3 = 0.113×75 = 8.475N. As per NCERT, applying relevant law/formula with correct units and sign convention leads to 8.5 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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Bernoulli's Theorem and Applications

A metal plate of area 0.05m2 moves over a liquid film (η\=0.02Pa s) of thickness 0.2mm at 0.5m/s. What is the force requ

Viscous force: F = ηvAl. η = 0.02Pa s, v = 0.5m/s, A = 0.05m2, l = 0.2×10−3m. F = 0.02×0.5×0.050.2×10−3 = 0.02×125 = 2.5N. As per NCERT, applying relevant law/formula with correct units and sign convention leads to 2.5 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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Equation of Continuity and Flow Rate

A plate of area 0.08m2 moves at 0.8m/s over a 0.7mm thick glycerine film (η\=0.83Pa s). What force is required?

Viscous force: F = ηvAl. η = 0.83Pa s, v = 0.8m/s, A = 0.08m2, l = 0.7×10−3m. F = 0.83×0.8×0.080.7×10−3 = 0.83×91.43 = 75.89N. As per NCERT, applying relevant law/formula with correct units and sign convention leads to 76 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 0.06m2 moves at 0.9m/s over a 0.5mm thick honey film (η\=0.2Pa s). What force is required?

Viscous force: F = ηvAl. η = 0.2Pa s, v = 0.9m/s, A = 0.06m2, l = 0.5×10−3m. F = 0.2×0.9×0.060.5×10−3 = 0.2×108 = 21.6N. As per NCERT, applying relevant law/formula with correct units and sign convention leads to 22 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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