Mechanical Properties of Fluids

8 NEET-UG practice questions on Mechanical Properties of Fluids, part of Physics. The first 8 are below; the first 5 with answers and explanations (tap Show answer after you have chosen), the rest in Learn with a free account.

1. Question 1 · Hard

   A wide open tank stands on level ground with its water surface kept 5 m above the ground. Water leaves through a small hole in the side wall, 1.8 m above the ground. Taking g = 10 m/s², how far from the base of the wall does the jet strike the ground?

   1. A4.8 m
   2. B2.4 m
   3. C3.6 m
   4. D6.0 m

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   Answer: A · 4.8 m

   The hole is 3.2 m below the surface, so v = √(2 × 10 × 3.2) = 8 m/s. Fall time = √(2 × 1.8/10) = 0.6 s, so the range = 8 × 0.6 = 4.8 m. Check: range = 2√(3.2 × 1.8) = 2 × 2.4 = 4.8 m.

   • B: This uses √(h₁h₂) without the factor 2.
   • C: This takes the head as the 1.8 m height of the hole above the ground.
   • D: This takes the head as the full 5 m.

   Remember this

   Range = 2√(h₁h₂), where h₁ is the depth of the hole and h₂ its height above the ground.

2. Question 2 · Medium

   Water flows through a horizontal pipe whose cross-section narrows in the ratio 3:1. The speed in the wide part is 2 m/s. Taking the density of water as 1000 kg/m³, what is the pressure difference between the wide and narrow parts?

   1. A16 kPa
   2. B2 kPa
   3. C32 kPa
   4. D8 kPa

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   Answer: A · 16 kPa

   Continuity: A₁v₁ = A₂v₂ gives v₂ = 3 × 2 = 6 m/s. Bernoulli: Δp = (1/2)ρ(v₂² − v₁²) = 500(36 − 4) = 16000 Pa = 16 kPa.

   • B: This uses the speed difference without squaring it.
   • C: This leaves out the factor 1/2 in Bernoulli's equation.
   • D: This squares the difference of speeds rather than taking the difference of squares.

   Remember this

   Use continuity for the new speed, then Bernoulli; pressure is lower where the fluid moves faster.

3. Question 3 · Medium

   To find the viscosity of a liquid of density 1500 kg/m³, a metal ball of density 6000 kg/m³ and diameter 2 mm is dropped into it. Once its speed is steady, the ball covers 10 cm in 5 s. Taking g = 10 m/s², what is the coefficient of viscosity?

   1. A2.0 Pa s
   2. B0.5 Pa s
   3. C0.67 Pa s
   4. D0.25 Pa s

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   Answer: B · 0.5 Pa s

   Terminal speed = 0.10/5 = 0.02 m/s and the radius is 10⁻³ m. Using η = 2r²(ρ − σ)g/(9v): η = 2 × 10⁻⁶ × 4500 × 10/(9 × 0.02) = 0.09/0.18 = 0.5 Pa s.

   • A: This uses the diameter in place of the radius.
   • C: This ignores buoyancy, using ρ instead of ρ − σ.
   • D: This leaves out the factor 2 in the formula.

   Remember this

   At terminal speed, weight = buoyancy + 6πηrv, so terminal speed varies as r²(ρ − σ).

4. Question 4 · Medium

   Match List-I with List-II. List-I (quantity) A. Speed of efflux from a hole at depth h in a tank B. Terminal speed of a small sphere of radius r in a liquid C. Gauge pressure at depth h in a liquid D. Capillary rise of a liquid in a tube of radius r List-II (proportional to) I. r² II. 1/r III. √h IV. h

   1. AA-IV, B-II, C-III, D-I
   2. BA-III, B-II, C-IV, D-I
   3. CA-III, B-I, C-IV, D-II
   4. DA-IV, B-I, C-III, D-II

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   Answer: C · A-III, B-I, C-IV, D-II

   Efflux speed is √(2gh). Terminal speed is 2r²(ρ − σ)g/(9η). Gauge pressure is ρgh, and capillary rise is 2S cos θ/(ρgr).

   • A: This makes both of the swaps above.
   • B: This swaps the terminal speed and the capillary rise.
   • D: This swaps the efflux speed and the gauge pressure.

   Remember this

   In a tube, the rise varies as 1/r; for a falling sphere, terminal speed varies as r².

5. Question 5 · Easy

   Bernoulli's equation in its standard form applies to which kind of flow?

   1. ASteady flow of a compressible, viscous fluid
   2. BTurbulent flow of an incompressible, viscous fluid
   3. CTurbulent flow of a compressible, non-viscous fluid
   4. DSteady flow of an incompressible, non-viscous fluid

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   Answer: D · Steady flow of an incompressible, non-viscous fluid

   The equation is energy conservation along a streamline, so it needs steady flow, constant density and no energy loss to viscosity.

   • A: Viscosity dissipates energy and compressibility changes the density.
   • B: Viscous, turbulent flow does not conserve mechanical energy.
   • C: Turbulent flow has no steady streamlines, and density changes here.

   Remember this

   Bernoulli's equation needs steady, incompressible and non-viscous flow, and it holds along a streamline.

6. Question 6 · Medium

   Water flows steadily through the horizontal pipe drawn, with vertical open tubes showing the pressure at two sections. Treating water as an ideal fluid and taking g = 10 m/s², find the level difference h.

   

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   1. A30 cm
   2. B20 cm
   3. C15 cm
   4. D5 cm

   Answer and explanation in LearnFree account

7. Question 7 · Easy

   A small steel ball is released from rest in a tall column of glycerine. Its speed against time is best shown by which graph?

   

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   1. AGraph A
   2. BGraph C
   3. CGraph B
   4. DGraph D

   Answer and explanation in LearnFree account

8. Question 8 · Hard

   Water escapes from a large open tank through a small side hole at the marked depth. Taking g = 10 m/s², how far from the wall does the jet land?

   

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   1. A2.4 m
   2. B6.0 m
   3. C3.6 m
   4. D4.8 m

   Answer and explanation in LearnFree account