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Mechanical Properties of Fluids appeared 31 times across 3 years — 3.6% of Physics. This question is from Viscosity and Terminal Velocity.

Year 2026 2025 2024 Total
Questions 9 14 8 31

In the experiment for measurement of viscosity η of given liquid with a ball having radius R , consider following statements. A. Graph between terminal velocity V and R will be a parabola B. The terminal velocities of different diameter balls are constant for a given liquid. C. Measurement of terminal velocity is dependent on the temperature. D. This experiment can be utilized to assess the density of a given liquid. E. If balls are dropped with some initial speed, the value of η will change. Choose the correct answer from the options given below:

Solution & Explanation

Related Formula
VT = (2)/(9) R² gη (d - ρ)
Core Logic

Let us check each statement sequentially:

Statement A: Since VT ∝ R², the graph between terminal velocity V and radius R is a quadratic curve, i.e., a parabola. (True)

Statement B: Different diameters imply different radii, hence terminal velocity will change. It is not constant. (False)

Statement C: Viscosity of a liquid is heavily temperature-dependent, hence VT changes with temperature. (True)

Statement D: Knowing the parameters allows calculation of liquid density ρ. (True)

Statement E: η is a material property of the fluid and does not change based on the initial dropping speed of the ball. (False)

Step 1: Final Conclusion

Statements A, C, and D are correct, which matches option (2).

Pattern Recognition

Terminal velocity problems rely entirely on parsing the proportional relations hidden in Stokes' Law formulation. Note that viscosity coefficient is an intrinsic characteristic parameter independent of kinematics.

Chapter Mix

Class 11 Physics: Mechanical Properties of Fluids

Reference Study Guides

More Mechanical Properties of Fluids Previous-Year Questions — Page 5

Q3 jee_main_2025_24_jan_morning Excess Pressure and Surface Tension
An air bubble of radius 0.1 cm lies at a depth of 20 cm below the free surface of a liquid of density 1000 kg/m³ If the pressure inside the bubble is 2100 N/m² greater than the atmospheric pressure, then the surface tension of the liquid in SI unit is (use g=10 m/s²)
  • A. 0.02
  • B. 0.1
  • C. 0.25
  • D. 0.04

Solution

Related Formula

The absolute pressure inside an air bubble submerged in a liquid is given by :

Pᵢₙ = P₀ + ρ gh + (2T)/(R)

where P₀ is atmospheric pressure, ρ is the liquid density, g is gravity, h is depth, T is surface tension, and R is the radius.

Core Logic

We are given that the difference between the inside pressure and atmospheric pressure is 2100 N/m²:

Pᵢₙ - P₀ = ρ gh + (2T)/(R) = 2100
Step 1: Numerical Evaluation

Substitute the given values into the relation :

ρ gh = 1000 × 10 × 0.20 = 2000 N/m²

Now find the excess pressure from surface tension:

(2T)/(R) = 2100 - 2000 = 100 N/m² T = (100 × R)/(2) = 50 × (0.1 × 10⁻²) = 0.05 N/m
Pattern Recognition

Total inside pressure accounts for both the hydrostatic pressure of the fluid column (ρ gh) and the spherical geometry boundary constraint pressure ((2T)/(R)).

Chapter Mix

Class 11 Physics: Mechanical Properties of Fluids

Q18 jee_main_2025_28_jan_evening Archimedes Principle
A 400g solid cube having an edge of length 10cm floats in water. How much volume of the cube is outside the water? (Given: density of water = 1000kgm⁻³ )
  • A. 1400cm³
  • B. 4000cm³
  • C. 400cm³
  • D. 600~cm³

Solution

Related Formula

By the law of flotation, the weight of a floating body must exactly balance the buoyant force exerted by the displaced fluid volume:

M · g = ρfluid · Vsubmerged · g
Core Logic

Given parameters:

  • Mass of the cube, M = 400 g = 0.4 kg
  • Total volume of the cube, Vtotal = (10 cm)³ = 1000 cm³ = 10⁻³ m³
  • Density of water, ρwater = 1000 kg/m³
  • Equating weight to buoyant force to find the submerged volume Vd :

0.4 = 1000 × Vsubmerged Vsubmerged = (0.4)/(1000) = 4 × 10⁻⁴ m³ = 400 cm³

Calculate the volume remaining outside the water surface :

Voutside = Vtotal - Vsubmerged Voutside = 1000 cm³ - 400 cm³ = 600 cm³
Pattern Recognition

The fraction of a floating body's volume that is submerged equals the ratio of the body's density to the fluid's density: VsubmergedVtotal = ρbodyρfluid. Here, the cube's effective density is 0.4 g/cm³, meaning 40% is submerged and 60% stays outside.

Chapter Mix

Class 11 Physics: Mechanical Properties of Fluids

Q jee_main_2025_29_jan_morning Pascal\'s Law
In a hydraulic lift, the surface area of the input piston is 6cm² and that of the output piston is 1500cm² . If 100N force is applied to the input piston to raise the output piston by 20cm , then the work done is ________ kJ.
Numerical Answer. Answer: 5 to 5

Solution

Related Formula
W = F₁ · s₁ = F₂ · s₂
Core Logic

By conservation of liquid volume displacement during output piston elevation :

A₁ · s₁ = A₂ · s₂ 6 · s₁ = 1500 · 20 s₁ = 5000 cm = 50 m

Work performed on input boundary matches :

W = F₁ · s₁ = 100 N · 50 m = 5000 J = 5 kJ

Alternatively via output force profile calculation:

Hydraulic lift work diagram allocation
Hydraulic lift work diagram allocation

F₂ = F₁ (A₂)/(A₁) = 100 (1500)/(6) = 25000 N W = F₂ · s₂ = 25000 · 0.2 = 5000 J = 5 kJ
Chapter Mix

Class 11 Physics: Mechanical Properties of Fluids

Q58 jee_main_2024_01_february_morning Bernoulli's Principle
A plane is in level flight at constant speed and each of its two wings has an area of 40~m². If the speed of the air is 180~km/h over the lower wing surface and 252~km/h over the upper wing surface, the mass of the plane is _______ kg. (Take air density to be 1~kg m⁻³ and g = 10~ms⁻²)
Numerical Answer. Answer: 9600 to 9600

Solution

Related Formula

Bernoulli's pressure balance equation for aerofoils:

Δ P = P₁ - P₂ = (1)/(2)ρ(v₂² - v₁²)

Dynamic Lift force balancing plane weight:

Flift = Δ P · Atotal = mg
Core Logic

Convert velocity limits to SI units:

v₁ = 180~km/h = 180 × (5)/(18) = 50~ms⁻¹ v₂ = 252~km/h = 252 × (5)/(18) = 70~ms⁻¹

Total effective wing area layout (2 wings):

Atotal = 2 × 40 = 80~m²
Step 1: Calculate Mass Balance

Substitute these values into the dynamic lift equation:

mg = (1)/(2) ρ (v₂² - v₁²) Atotal m(10) = (1)/(2) × 1 × (70² - 50²) × 80 10m = 40 × (4900 - 2500) = 40 × 2400 = 96000 m = 9600~kg
Pattern Recognition

Remember to multiply individual wing areas by 2 for standard multi-wing lift structures (Atotal = 2A).

Chapter Mix

Class 11 Physics: Mechanical Properties of Fluids

Q jee_main_2024_29_january_evening Surface Tension
A small liquid drop of radius R is divided into 27 identical liquid drops. If the surface tension is T, then the work done in the process will be:
  • A. 8π R² T
  • B. 3π R² T
  • C. (1)/(8)π R² T
  • D. 4π R² T

Solution

Related Formula

The work done in changing the surface area of a liquid is given by:

W = T · Δ A

where:

  • T is the surface tension of the liquid.
  • Δ A = Af - Aᵢ is the change in the total surface area.
Core Logic

Since the total volume remains constant during splitting:

Vᵢ = Vf

(4)/(3)π R³ = 27 × (4)/(3)π r³ R³ = 27r³ r = (R)/(3)
Step 1: Calculate the Change in Surface Area

Initial surface area of the single drop:

Aᵢ = 4π R²

Final surface area of 27 small drops:

Af = 27 × (4π r²) = 27 × 4π ((R)/(3))² Af = 27 × 4π (R²)/(9) = 12π R²

Change in surface area:

Δ A = Af - Aᵢ = 12π R² - 4π R² = 8π R²
Step 2: Calculate Work Done

Substituting the change in area into the work done formula:

W = T · Δ A = 8π R² T
Pattern Recognition

For splitting a large drop of radius R into n identical small drops, the change in surface area is given by Δ A = 4π R² (n1/3 - 1). Substituting n = 27 gives Δ A = 4π R² (3 - 1) = 8π R², leading immediately to 8π R² T.

Chapter Mix

Class 11 Physics: Mechanical Properties of Fluids

More Mechanical Properties of Fluids Questions — jee_main_2025_28_jan_morning

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