Mechanical Properties of Fluids — Class 11 MCQs with Answers

Mechanical Properties of Fluids — important questions & MCQs with answers (Class 11 Physics)

13 solved questions from this chapter's difficulty levels, each with its answer and explanation. The other 53 are timed and scored when you sign in.

1. Q1Easy

   SI unit of pressure:

   A.Joule

   B.Pascal✓ Correct

   C.Newton

   D.Watt

   Answer: B. Pascal

   Explanation: Pressure's SI unit is the pascal: 1 Pa = 1 N/m², force per area. Joule is energy and Watt is power — a common mix-up, but pressure is neither.

2. Q2Easy

   Pressure at depth h in fluid (density ρ):

   A.g h

   B.ρ h

   C.ρ g h✓ Correct

   D.ρ g

   Answer: C. ρ g h

   Explanation: Hydrostatic pressure at depth h in a fluid of density ρ is P = ρgh, combining density, gravity, and depth — dropping g (leaving just ρh) is the frequent error since g is rarely written explicitly.

3. Q3Easy

   Pascal's law:

   A.Pressure depends on shape

   B.Pressure applied to enclosed fluid transmits equally in all directions✓ Correct

   C.Variable

   D.Only at top

   Answer: B. Pressure applied to enclosed fluid transmits equally in all directions

   Explanation: Pascal's law: pressure applied to an enclosed fluid is transmitted equally in all directions, unchanged in magnitude — not just to the top, and not dependent on the container's shape.

4. Q4Easy

   Archimedes' principle: buoyant force equals:

   A.Weight of displaced fluid✓ Correct

   B.Total weight

   C.Volume

   D.Density

   Answer: A. Weight of displaced fluid

   Explanation: Archimedes' principle: the buoyant force on a submerged or floating body equals the weight of the fluid it displaces, ρ_fluid·V·g — not the body's own total weight.

5. Q5Easy

   Viscosity is:

   A.Internal friction in fluid✓ Correct

   B.External force

   C.Buoyancy

   D.Pressure

   Answer: A. Internal friction in fluid

   Explanation: Viscosity is the internal friction within a fluid — the resistance one layer offers to sliding past an adjacent layer — distinct from buoyancy (an upward force) or pressure (force per area).

6. Q6Medium

   Force 100 N on area 0.5 m². Pressure:

   A.50 Pa

   B.100 Pa

   C.200 Pa✓ Correct

   D.0.5 Pa

   Answer: C. 200 Pa

   Explanation: Pressure P = F/A = 100 N ÷ 0.5 m² = 200 Pa. Dividing the wrong way (0.5/100) or forgetting to divide gives 50 Pa or 100 Pa — check units cancel to N/m² before picking an answer.

7. Q7Medium

   Pressure at 10 m depth in water (ρ = 1000, g = 10):

   A.10⁵ Pa✓ Correct

   B.10⁴

   C.10⁶

   D.10³

   Answer: A. 10⁵ Pa

   Explanation: Hydrostatic pressure P = ρgh = 1000 kg/m³ × 10 m/s² × 10 m = 1×10⁵ Pa, using g = 10 m/s² as given here — dropping a power of ten in the multiplication gives the tempting but wrong 10⁴ Pa.

8. Q8Medium

   Hydraulic lift: small piston area 1 cm², force 10 N. Large piston area 100 cm². Force lifted:

   A.10 N

   B.1000 N✓ Correct

   C.100 N

   D.Cannot determine

   Answer: B. 1000 N

   Explanation: Pascal's law keeps pressure equal on both pistons: F₁/A₁ = F₂/A₂, so F₂ = 10 N × (100 cm²/1 cm²) = 1000 N. Using the area ratio the wrong way round gives the tempting but wrong 100 N.

9. Q9Medium

   Body of volume 100 cm³ in water (ρ = 1000). Buoyant force (g = 10):

   A.100 N

   B.10 N

   C.1 N✓ Correct

   D.Cannot determine

   Answer: C. 1 N

   Explanation: Buoyant force = ρ_water·V·g = 1000 kg/m³ × 100×10⁻⁶ m³ × 10 m/s² = 1 N. Forgetting to convert 100 cm³ to 10⁻⁴ m³ before multiplying is the common slip giving 10 N or 100 N instead.

10. Q10Medium

    Coefficient of viscosity is greater for:

    A.Liquids than gases✓ Correct

    B.Gases than liquids

    C.Solids

    D.Equal

    Answer: A. Liquids than gases

    Explanation: Liquid molecules sit close together with strong cohesive forces, giving liquids far higher viscosity than gases, whose widely-spaced molecules barely resist shear — assuming 'thinner' gases are more viscous is the wrong intuition.

11. Q11Hard

    Archimedes' principle: buoyant force =

    A.Weight of body

    B.Weight of displaced fluid✓ Correct

    C.Mass of fluid

    D.Volume × pressure

    Answer: B. Weight of displaced fluid

    Explanation: Archimedes' principle: buoyant force equals the weight of fluid displaced, ρ_fluid·V_displaced·g — not the body's own weight or the mass of the fluid, which is the tempting mix-up.

12. Q12Hard

    In U-tube manometer, mercury difference of 5 cm indicates pressure difference of:

    A.ρ g h (Hg) = 13600 × 9.8 × 0.05 ≈ 6664 Pa✓ Correct

    B.5 mm

    C.100 Pa

    D.Cannot determine

    Answer: A. ρ g h (Hg) = 13600 × 9.8 × 0.05 ≈ 6664 Pa

    Explanation: Pressure difference from a mercury column is ΔP = ρ_Hg·g·h = 13600 kg/m³ × 9.8 m/s² × 0.05 m ≈ 6664 Pa. Forgetting to convert 5 cm to 0.05 m before multiplying is the frequent slip here.

13. Q13Hard

    Hydraulic press with piston ratio 1:100. Force ratio:

    A.Cannot determine

    B.1:100

    C.1:1

    D.100:1 (force multiplied)✓ Correct

    Answer: D. 100:1 (force multiplied)

    Explanation: By Pascal's law, pressure F/A is the same throughout the fluid, so force is proportional to piston area: with areas in ratio 1:100, the resulting force is multiplied 100:1 on the larger piston — this is the whole point of a hydraulic press.

Mechanical Properties of Fluids — FAQs

More Class 11 Physics chapters

• 01Physical World
• 02Units and Measurements
• 03Motion in a Straight Line
• 04Motion in a Plane
• 05Laws of Motion
• 06Work, Energy and Power

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