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NEET Physics: Stokes' law Practice Questions

15 free multiple-choice questions on Stokes' law (Properties of Solids and Liquids) for NEET Physics, each with the correct answer and a step-by-step explanation. Attempt a question, then reveal the solution to check your reasoning.

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  1. Q1. In the context of fluid dynamics, what quantity is directly proportional to the resistance experienced by a spherical object moving slowly through a viscous medium according to Stokes' Law?

    • Athe radius of the object
    • Bthe cube of the radius
    • Cthe velocity of the object
    • Dthe square of the velocity
    Show answer & explanation

    Correct answer: C — the velocity of the object

    Stokes' Law states that the drag force is directly proportional to the velocity of the object. Thus, the drag force is directly proportional to the velocity of the object (F_d ∝ v).

  2. Q2. If the velocity of a sphere moving through a viscous fluid is doubled, the viscous drag force exerted on it will change by a factor of:

    • A2
    • B8
    • C4
    • D1/2
    Show answer & explanation

    Correct answer: C — 4

    Since drag force is directly proportional to velocity (F_D ∝ v), doubling the velocity will double the drag force.

  3. Q3. The proportionality constant in Stokes' Law is directly related to which property of the fluid?

    • Aviscosity of the fluid
    • Bcompressibility of the fluid
    • Csurface tension of the fluid
    • Ddensity of the fluid
    Show answer & explanation

    Correct answer: A — viscosity of the fluid

    The constant factor in Stokes' Law is directly proportional to the coefficient of viscosity (η) of the fluid.

  4. Q4. Stokes' Law applies to the motion of objects under which specific flow condition?

    • Aslow and laminar flow
    • Bhigh-speed turbulent flow
    • Cnon-Newtonian flow
    • Dhighly compressible flow
    Show answer & explanation

    Correct answer: A — slow and laminar flow

    Stokes' Law is strictly valid only for objects moving slowly through a viscous fluid under conditions of laminar flow.

  5. Q5. Which physical property of the fluid is the primary factor that determines the magnitude of the drag force in Stokes' law?

    • AFluid density
    • BFluid compressibility
    • CFluid viscosity
    • DFluid pressure
    Show answer & explanation

    Correct answer: C — Fluid viscosity

    Viscosity (η) is the measure of a fluid's resistance to flow and is the key property that quantifies the viscous drag in Stokes' law.

  6. Q6. In the context of fluid dynamics, the relationship described by Stokes' Law is an example of which type of proportionality regarding the resistive interaction?

    • ADirect proportionality
    • BSquare proportionality
    • CExponential proportionality
    • DInverse proportionality
    Show answer & explanation

    Correct answer: A — Direct proportionality

    Stokes' Law is F ∝ v (linear relationship with velocity) and F ∝ r (linear relationship with radius). The force is directly proportional to both the velocity and the radius.

  7. Q7. The mathematical form of Stokes' law for the drag force (F) acting on a sphere of radius (r) moving at velocity (v) in a viscous fluid of viscosity (η) is given by:

    • AF = 3 πηr v²
    • BF = 6 πηv² / r
    • CF = 12 πηr v
    • DF = 6 πηr v
    Show answer & explanation

    Correct answer: D — F = 6 πηr v

    The standard formula for Stokes' Law is F = 6 πηr v.

  8. Q8. The drag force calculated using Stokes' law is directly proportional to the radius of the sphere. If the radius of a sphere is halved while keeping the velocity and viscosity constant, the drag force will:

    • AQuadruple
    • BHalve
    • CRemain the same
    • DDouble
    Show answer & explanation

    Correct answer: B — Halve

    The formula involves r linearly (F_D ∝ r). Halving r will halve the drag force.

  9. Q9. Which physical regime is required for Stokes' law to be an accurate description of the motion of a sphere in a viscous fluid?

    • AHigh Reynolds number flow
    • BTurbulent flow
    • CVery high velocity flow
    • DLow Reynolds number flow
    Show answer & explanation

    Correct answer: D — Low Reynolds number flow

    Stokes' law is specifically valid only when the flow is laminar and the Reynolds number is very small (low Reynolds number flow).

  10. Q10. When a small spherical object moves through a viscous fluid at a constant velocity, the drag force exerted on it is directly proportional to which of the following physical quantities?

    • AThe radius of the sphere
    • BThe square of the velocity
    • CThe density of the fluid
    • DThe volume of the sphere
    Show answer & explanation

    Correct answer: A — The radius of the sphere

    Stokes' Law states that the drag force (F) is proportional to the radius (r), the velocity (v), and the viscosity (η) of the fluid (F ∝ r v η). In this scenario, since r and η are considered constant for the proportionality relationship being tested, the drag force is directly proportional to the velocity (v). However, among the given choices, we must identify which parameter from the general relationship dominates the dependency when considering the physical factors of the movement and the object's geometry. Since the drag force depends linearly on velocity, and the relationship involves the geometrical size, the direct proportionality holds for the velocity component when other factors are fixed. (Note: In the context of the fundamental proportionality F ∝ v, we check which variable *must* be included in the relationship. The simplest proportional relationship is F ∝ v when r and η are held constant, but the provided options test the dependency on the factors.) Let's rephrase to ensure the correct answer tests the proportionality derived from F=6πηr v. The drag force is directly proportional to velocity.

  11. Q11. Stokes' law describes the drag force experienced by a sphere moving through a viscous fluid. This drag force is directly proportional to which of the following parameters?

    • AThe velocity of the sphere
    • BThe acceleration of the sphere
    • CThe surface area of the sphere
    • DThe density of the sphere
    Show answer & explanation

    Correct answer: A — The velocity of the sphere

    Stokes' law states that the drag force (F_D) is directly proportional to the velocity (v) of the object. F_D = 6 πηr v.

  12. Q12. According to the mathematical formulation of Stokes' Law, the relationship between the drag force and the fluid properties and object properties is governed by which mathematical dependency?

    • AF_d ∝ (η+ r) v
    • BF_d ∝ η/ (r v)
    • CF_d ∝ ηr v
    • DF_d ∝ ηr² v
    Show answer & explanation

    Correct answer: C — F_d ∝ ηr v

    The mathematical statement of Stokes' Law is F_d = 6 πηr v. This shows the force is proportional to the product of viscosity (η), radius (r), and velocity (v).

  13. Q13. The magnitude of the viscous resistance force exerted by a fluid on a spherical object is generally proportional to which dimension of the object?

    • AVolume
    • BArea
    • CRadius
    • DLength
    Show answer & explanation

    Correct answer: C — Radius

    For spherical objects under Stokes' Law, the drag force is proportional to the radius of the sphere.

  14. Q14. Stokes' law is applicable for the drag force exerted on a spherical object moving through a fluid under which condition?

    • AStatic fluid
    • BHigh Reynolds number
    • CCompressible fluid
    • DLow Reynolds number
    Show answer & explanation

    Correct answer: D — Low Reynolds number

    Stokes' law is derived for viscous flow, which occurs when the flow is slow and viscous, corresponding to a low Reynolds number.

  15. Q15. If the viscosity of the fluid surrounding a sphere is increased by a factor of 2, while the velocity remains constant, how does the resulting drag force change?

    • AIt is halved
    • BIt is quadrupled
    • CIt remains unchanged
    • DIt is doubled
    Show answer & explanation

    Correct answer: D — It is doubled

    Since drag force is directly proportional to viscosity (F_D ∝ η), doubling the viscosity doubles the drag force.

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