NEETAceToday's NEET Daily

Fluid pressure, Pascal’s law and effect of gravity: NEET MCQs with answers

54 questions on this topic of Properties of Solids and Liquids (NEET 2027 syllabus). Here are 12; tap one to see its answer and explanation.

Practise Properties of Solids and Liquids freeAll Properties of Solids and Liquids questions

Free with a Google sign-in; NEET Daily needs no sign-in at all.

easy

1. In a hydraulic lift, the diameters of the effort piston and the load piston are in the ratio 1 : 5. If a force of 120 N is applied downward on the effort piston, causing it to move down by 50 cm, what is the work done on the load assuming no friction or fluid compressibility?

  1. 300 J
  2. 60 J
  3. 1500 J
  4. 12 J
Show answer and explanation

Answer: (B) 60 J

According to Pascal's principle and conservation of energy for an ideal hydraulic machine, the work done on the input piston equals the work done on the output piston (Work = Force × displacement). Here, Work = 120 N × 0.50 m = 60 J. Although the force is multiplied by a factor of 25, the displacement of the load piston decreases by the same factor of 25, keeping the work done equal to 60 J.

medium

2. A container filled with liquid of density ρ is accelerated vertically downwards with acceleration a = g/3. What is the gauge pressure at a depth h below the free surface of the liquid?

  1. ρgh
  2. (4/3) ρgh
  3. (2/3) ρgh
  4. (1/3) ρgh
Show answer and explanation

Answer: (C) (2/3) ρgh

When the container accelerates downward with acceleration a, the effective acceleration due to gravity is g_eff = g - a = g - g/3 = (2/3)g. Hence, the gauge pressure at depth h is P_gauge = ρ g_eff h = (2/3) ρgh.

hard

3. An open cubical container of side 80 cm is half filled with water. It is placed on an inclined plane that makes an angle of 37° with the horizontal. If the container slides down the frictionless incline freely, the angle that the free surface of water makes with the inclined plane is:

  1. 90°
  2. 37°
  3. 53°
  4. 0°
Show answer and explanation

Answer: (D) 0°

When sliding freely down a frictionless incline of angle θ, the acceleration along the incline is a = g sin θ. In the non-inertial frame of the container, the effective gravity components are g_parallel = g sin θ - a = 0, and g_perpendicular = g cos θ directed into the incline. Since the effective acceleration is strictly perpendicular to the incline, the equilibrium free surface aligns perpendicular to the effective gravity, which means it is parallel to the inclined plane (angle = 0°).

medium

4. A tank is filled with three immiscible liquids of equal volume: liquid 1 of density ρ, liquid 2 of density 2ρ, and liquid 3 of density 3ρ. The tank has uniform cross-section and total depth 3h. What is the gauge pressure at the bottom of the tank?

  1. 3 ρgh
  2. 6 ρgh
  3. 2 ρgh
  4. 14 ρgh
Show answer and explanation

Answer: (B) 6 ρgh

Since each liquid occupies an equal volume in a tank of uniform cross-section, each liquid layer has the same depth h. The liquids settle in order of density: top layer of density ρ, middle layer of 2ρ, and bottom layer of 3ρ. The total gauge pressure at the bottom is ΔP = ρgh + (2ρ)gh + (3ρ)gh = 6ρgh.

easy

5. Taking the density of water as 1000 kg/m³ and g = 10 m/s², the gauge pressure at a depth of 2 m in a lake is:

  1. 20000 Pa
  2. 2 × 10⁵ Pa
  3. 2000 Pa
  4. 1.2 × 10⁵ Pa
Show answer and explanation

Answer: (A) 20000 Pa

Gauge pressure = ρgh = 1000 × 10 × 2 = 20000 Pa (atmospheric pressure is not included in gauge pressure).

hard

6. A U-tube of uniform cross-sectional area contains liquid of density ρ. The horizontal limb has a length L, and the tube is accelerated horizontally along the direction of the horizontal limb with an acceleration 'a'. What is the difference in heights (Δh) of the liquid levels in the two vertical limbs?

  1. aL / (2g)
  2. gL / a
  3. 2aL / g
  4. aL / g
Show answer and explanation

Answer: (D) aL / g

Consider a horizontal segment of liquid of length L in the bottom tube. The horizontal pressure difference across it must provide the accelerating force: (P₁ - P₂)A = (ρLA)a, which gives P₁ - P₂ = ρaL. Since the vertical limbs are open, P₁ - P₂ = ρgΔh. Equating both expressions gives ρgΔh = ρaL, so Δh = aL / g.

easy

7. Consider the following statements regarding pressure in a fluid at rest under gravity: Statement I: The pressure is identical at all points lying on the same horizontal plane in a continuous, single static fluid. Statement II: The hydrostatic force exerted on the base of a container depends on the shape of the container and not merely on the base area and liquid depth. Choose the correct option:

  1. Both Statement I and Statement II are correct
  2. Statement I is correct but Statement II is incorrect
  3. Statement I is incorrect but Statement II is correct
  4. Both Statement I and Statement II are incorrect
Show answer and explanation

Answer: (B) Statement I is correct but Statement II is incorrect

Statement I is correct because in a static, continuous fluid of uniform density, there is no horizontal acceleration, so pressure must be equal across horizontal planes. Statement II is incorrect because the force on a horizontal flat base of area A is F = P × A = (hρg)A, which is independent of the overall shape of the walls (hydrostatic paradox).

easy

8. Taking the density of water as 1000 kg/m³ and g = 10 m/s², the gauge pressure at a depth of 14 m in a lake is:

  1. 1.4 × 10⁵ Pa
  2. 1.4 × 10⁶ Pa
  3. 14000 Pa
  4. 2.4 × 10⁵ Pa
Show answer and explanation

Answer: (A) 1.4 × 10⁵ Pa

Gauge pressure = ρgh = 1000 × 10 × 14 = 1.4 × 10⁵ Pa (atmospheric pressure is not included in gauge pressure).

easy

9. Which of the following instruments works directly on Pascal's principle?

  1. Hydraulic brakes
  2. Venturimeter
  3. Fortin's barometer
  4. Pitot tube
Show answer and explanation

Answer: (A) Hydraulic brakes

Hydraulic brakes operate on Pascal's principle, which states that an externally applied pressure to an enclosed static fluid is transmitted undiminished throughout the fluid. Venturimeter works on Bernoulli's principle, while barometers measure atmospheric pressure directly via hydrostatic balance.

easy

10. A closed rigid vessel is completely filled with water at room temperature. A small pressure pulse ΔP is applied at one point on the boundary of the vessel. Which of the following correctly describes how ΔP is transmitted through the fluid?

  1. It decreases inversely with the square of the distance from the point of application
  2. It is transmitted only in the direction of the applied force
  3. It is absorbed uniformly by the compressibility of water, vanishing near the walls
  4. It is transmitted undiminished to every portion of the fluid and to the walls of the vessel
Show answer and explanation

Answer: (D) It is transmitted undiminished to every portion of the fluid and to the walls of the vessel

By Pascal's principle, any change in pressure applied to a completely enclosed fluid is transmitted undiminished to every portion of the fluid and to the walls of the containing vessel.

medium

11. A vertical dam wall of height H and width W retains water of density ρ up to its top edge. The total horizontal force exerted by the water on the dam wall is F. At what depth from the free water surface does the effective line of action of this resultant hydrostatic force act?

  1. 2H/3
  2. H/2
  3. H/3
  4. 3H/4
Show answer and explanation

Answer: (A) 2H/3

The pressure varies linearly with depth y as P(y) = ρgy. The total force is F = ∫ ρgy W dy = (1/2)ρgWH². The torque about the top surface is τ = ∫ y dF = ∫ ρgy² W dy = (1/3)ρgWH³. The line of action is at depth y_c = τ/F = [(1/3)ρgWH³] / [(1/2)ρgWH²] = 2H/3.

easy

12. A hydraulic lift has two pistons with circular cross-sections of radii 5 cm and 20 cm respectively. What force must be applied to the smaller piston to lift an automobile of mass 1600 kg placed on the larger piston? (Take g = 10 m/s²)

  1. 1000 N
  2. 100 N
  3. 400 N
  4. 2500 N
Show answer and explanation

Answer: (A) 1000 N

According to Pascal's law, pressure is transmitted equally: F₁/A₁ = F₂/A₂. Thus, F₁ = F₂ × (A₁/A₂) = (1600 × 10) × (π × 5²)/(π × 20²) = 16000 × (1/16) = 1000 N.

Keep going with Properties of Solids and Liquids. All 429 questions with instant answers, your mistakes saved for revision and your accuracy by topic.
Start practising

Other topics in Properties of Solids and Liquids