Free Fluid Dynamics MCQs with Answers
363 Fluid Dynamics MCQs from Physics, each with the correct answer and a written explanation of why it is correct. Free and unlimited, with no account needed.
Fluid flow is described through speed, pressure and density, including steady flow and the equation of continuity for conserving mass. Bernoulli's equation relates pressure, speed and height, while fluid drag and terminal velocity explain why a falling object eventually moves at constant speed when drag balances its weight.
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Read the Fluid Dynamics notesFree MDCAT chapter notes with key terms363 questions · page 10 of 19
181. If the viscosity of a fluid increases, the velocity boundarylayer formed over a surface becomes:
- A. More
- B. Less
- C. No effect
- D. Unpredictable
Explanation: Higher viscosity enhances momentum diffusion from the wall into the flow, producing a thicker boundary layer compared with lower-viscosity…
Correct answer: More- A. 25.6 m/s
- B. 3.45 m/s
- C. 1.23 m/s
- D. 1.592 m/s
Explanation: Correct calculation: mass flow = 30 kg/60 s = 0.5 kg/s ⇒ volumetric Q = 0.5/1000 = 5×10⁻⁴ m³/s.
Correct answer: 1.592 m/s- A. Law of conservation of mass
- B. Law of conservation of energy
- C. Law of conservation of power
- D. Law of conservation of volume
Explanation: Bernoulli's equation is derived from energy conservation for a fluid element, equating pressure energy, potential energy and kinetic…
Correct answer: Law of conservation of energy- A. Volume
- B. Area
- C. Pressure
- D. Velocity
Explanation: ρgh has units (kg/m³)(m/s²)(m) = kg/(m·s²) = N/m², which is Pascal, the unit of pressure.
Correct answer: Pressure- A. Object will become stationary
- B. Object will fall freely
- C. Object will fall with terminal velocity
- D. Object will fall with critical velocity
Explanation: When drag force equals weight, net force is zero so acceleration ceases and the object falls at constant terminal velocity.
Correct answer: Object will fall with terminal velocity- A. 1.5 cm/s
- B. 6 cm/s
- C. 24 cm/s
- D. 32 cm/s
Explanation: Combining 8 equal drops doubles the radius (since volume ∝ r³). Terminal velocity scales ∝ r², so new velocity = 4×6 = 24 cm/s.
Correct answer: 24 cm/s- A. vₜ/r = constant
- B. vₜr= constant
- C. vₜ = constant
- D. vₜ/r2= constant
Explanation: From Stokes' law vt= (2/9)(ρ −ρ ) g r² / η, so vt∝ r². Therefore vt/r² is constant for given fluid and material properties.
Correct answer: vₜ/r2= constant- A. 1:2
- B. 4:1
- C. 1 : √3
- D. 2:1
Explanation: For similar-density spheres under Stokes-like conditions, Vt ∝ r²; however if regime gives Vt ∝ √r (inertial-balance approximations) some…
Correct answer: 1 : √3- A. Laminar flow
- B. Turbulent flow
- C. Streamline flow
- D. Both A & C
Explanation: Low-speed, low-Reynolds-number flows are laminar and are often described as streamline flow; both terms apply.
Correct answer: Both A & C- A. Laminar flow
- B. Turbulent flow
- C. Streamline flow
- D. Both A and C
Explanation: Laminar flow refers to a smooth, orderly flow of fluid where layers move parallel to each other with minimal disruption, typically…
Correct answer: Laminar flow- A. 0
- B. g
- C. 6πηrV - mg
- D. a = g - 6πηrV/m
Explanation: Net force = drag − weight = 6π η r V − m g; acceleration a = F = (6π η r V)/m − g.
Correct answer: a = g - 6πηrV/m192. If a fluid drops or object moves downwards with constantspeed through a fluid, it's acceleration is:
- A. g
- B. a > g
- C. 0
- D. constant
Explanation: Constant speed implies zero acceleration (no change of velocity).
Correct answer: 0- A. 4Vt
- B. 2Vt
- C. 8Vt
- D. Vt
Explanation: Combining 8 identical droplets doubles the radius (volume scales by 8 ⇒ r new = 2 r). Since Vt ∝ r², V new = (2²) Vt = 4 Vt.
Correct answer: 4Vt- A. Law of conservation of mass
- B. Law of conservation of energy
- C. Law of conservation of charge
- D. None of these
Explanation: Continuity (A₁v₁ = A₂v₂) ensures mass is conserved in steady incompressible flow: mass entering equals mass leaving.
Correct answer: Law of conservation of mass- A. Gravitational force
- B. Electromagnetic interactions
- C. Cohesive force
- D. None
Explanation: Viscosity arises because adjacent layers of a fluid exchange momentum through intermolecular electromagnetic forces.
Correct answer: Electromagnetic interactions- A. 1:4
- B. 4:1
- C. 2:1
- D. 1:2
Explanation: For equal masses but different densities, radius affects terminal velocity through complex dependence; under typical assumptions Vt scales…
Correct answer: 4:1- A. 32 m/s
- B. 16 m/s
- C. 8 m/s
- D. 64 m/s
Explanation: Splitting into 8 reduces each small drop's radius to r/2 (since volume ∝ r³).
Correct answer: 8 m/s- A. 4:1
- B. 1:4
- C. 1:2
- D. 2:1
Explanation: Continuity: v1/v2 = (A2/A1) = (r2²/r2²). If v1:v2 = 4:1 ⇒ (r2/r1)² = 4 ⇒ r2/r1 = 2 ⇒ r1:r2 = 1:2
Correct answer: 2:1- A. High Speed
- B. Low Speed
- C. Certain acceleration
- D. Constant Speed
Explanation: When the drag force equals the weight of the droplet, the net force becomes zero.
Correct answer: Constant Speed- A. 5m/s
- B. 10m/s
- C. 2m/s
- D. 50m/s
Explanation: v2=u2+2as→v2 =0+2(5)(10)→v2=100→v= 10 m/s. As it is a numerical, it can have only one possible answer.
Correct answer: 10m/s