Fluid Dynamics

Fluid Dynamics MDCAT MCQs with answers

18 past paper MCQs from Physics unit 5, Fluid Dynamics, across 5 topics. They are arranged topic by topic; bigger topics show a sample here and link to their full set and to study notes. Tap “Show answer” for the correct option and a short solution.

Practise as a quiz

Fluid Drag and Terminal Velocity

1.When a heavy coin falls a short distance towards the ground it does not reach terminal velocity. Why is this so? (MDCAT 2022)

  1. the coin has not hit the ground
  2. the weight of the coin is equal to the air resistance
  3. the weight of the coin increases as the air resistance increases
  4. the weight of the coin is more than the air resistance
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Correct answer: (d) the weight of the coin is more than the air resistance

Terminal velocity is reached only when the drag has grown equal to the weight, and over a short fall it has not.

2.A ball of weight Fg is falling vertically downward through air. If the drag force acting on it at some instant is Fd, what is the Fnet (net force) on the ball? (KMU MDCAT 2025)

  1. Fg + Fd
  2. Fg - Fd
  3. Fd - Fg
  4. Fd/Fg
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Correct answer: (b) Fg - Fd

Drag acts upwards against the fall, so the net downward force is the weight less the drag.

3.A body of mass 10 kg is falling through a viscous medium and reached terminal velocity. The net force on the body will be: (SIBA MDCAT 2025)

  1. 0 N
  2. 9.8 N
  3. 98 N
  4. 980 N
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Correct answer: (a) 0 N

At terminal velocity the drag and upthrust balance the weight, so there is no net force.

4.When a droplet reaches terminal velocity, its acceleration is: (SIBA MDCAT 2025)

  1. Zero
  2. Variable
  3. Not changed
  4. Negative
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Correct answer: (a) Zero

Terminal velocity is a steady velocity, so the acceleration has fallen to zero.

Fluid Drag and Terminal Velocity notes →

Fluid Flow

5.A fluid is flowing through a tube, to undergo transition from laminar to turbulent flow it's velocity must be: (UHS MDCAT 2025)

  1. Slightly less than critical velocity
  2. equal to critical velocity
  3. greater than critical velocity
  4. increasing gradually but less than critical velocity
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Correct answer: (c) greater than critical velocity

Flow stays laminar up to the critical velocity and turns turbulent once that value is passed.

6.Most kinds of fluid flow are turbulent rather than laminar because of: (KMU MDCAT 2025)

  1. Zero viscosity
  2. Very low velocities
  3. High velocities
  4. No resistance
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Correct answer: (c) High velocities

Beyond the critical speed the layers break up, and most real flows are above it.

7.In laminar flow of fluid, its adjacent layers: (SIBA MDCAT 2025)

  1. Resist each other
  2. Mix with each other
  3. Slide smoothly pass each other
  4. Produce turbulence
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Correct answer: (c) Slide smoothly pass each other

In laminar flow the layers glide over one another without mixing.

8.When fluid is incompressible, the quantity is constant is: (UHS MDCAT 2016)

  1. Mass
  2. Density
  3. Pressure
  4. Force
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Correct answer: (b) Density

An incompressible fluid is one whose density does not change however it is squeezed.

Fluid Flow notes →

Equation of Continuity

9.An incompressible fluid flows through a pipe that becomes narrower in one section. The fluid speed in that region increases in that region to maintain: (UHS MDCAT 2025)

  1. Constant pressure
  2. constant energy
  3. constant mass flow rate
  4. constant volume
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Correct answer: (c) constant mass flow rate

What enters the pipe each second must leave it, so a narrower section is passed at a greater speed.

10.According to law of continuity, when the cross-sectional area of a pipe decreases, the fluid velocity: (KMU MDCAT 2025)

  1. Increases
  2. Decreases
  3. Remains the same
  4. Becomes zero
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Correct answer: (a) Increases

The product of area and speed is constant, so a narrower pipe is passed faster.

11.Water flows through a pipe of 0.02 m^2 with a speed of 3 m/s. The pipe narrows to 0.01 m^2. The speed in narrow section is: (SZABMU MDCAT 2025)

  1. 1.5 m/s
  2. 3 m/s
  3. 6 m/s
  4. 9 m/s
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Correct answer: (c) 6 m/s

$A_1v_1=A_2v_2$, so $0.02\times3=0.01\times v_2$ and $v_2$ is $6\,\mathrm{m\,s^{-1}}$.

Equation of Continuity notes →

Bernoulli’s Equation

12.In a pipe of varying cross-section as fluid enters the narrower region, it exhibits: (UHS MDCAT 2025)

  1. high velocity, high pressure
  2. high velocity, low pressure
  3. low velocity, high pressure
  4. low velocity, low pressure
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Correct answer: (b) high velocity, low pressure

Bernoulli’s equation trades pressure for speed, so the fast narrow section is the low pressure one.

13.Water flows steadily through a pipe that gradually narrows. At the wider end, the velocity of water is 1m/s, at the narrower end, the velocity is 3m/s. Which statement is CORRECT about the pressure in the narrower end compared to the wider end? (KMU MDCAT 2025)

  1. Pressure is lower at the narrow end because velocity is higher
  2. Pressure is higher at the narrow end because velocity is higher
  3. Pressure is the same at both ends since flow is continuous
  4. Pressure is independent of velocity of water
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Correct answer: (a) Pressure is lower at the narrow end because velocity is higher

Bernoulli’s equation trades pressure for speed, so the faster narrow end is at the lower pressure.

14.The increase in kinetic energy associated with decreased pressure of a fluid in a horizontal pipe is a consequence of the: (SIBA MDCAT 2025)

  1. Bernoulli's Principle
  2. Equation of continuity
  3. Pascal's principle
  4. Torricelli's theorem
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Correct answer: (a) Bernoulli's Principle

Bernoulli’s principle is the statement that pressure falls where the speed of a fluid rises.

All 5 Bernoulli’s Equation MCQs → Bernoulli’s Equation notes →

Bernoulli’s Effect and Blood Physics

15.The curved shape of an airplane wing causes air to move faster over the top surface. This leads to: (UHS MDCAT 2025)

  1. greater pressure on the top
  2. lower pressure on the top
  3. equal pressure on both sides
  4. zero pressure above the wing
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Correct answer: (b) lower pressure on the top

Faster air over the curved upper surface leaves a lower pressure there, and the difference is the lift.

16.In the human circulatory system, turbulent blood flow is most likely to occur when the: (SZABMU MDCAT 2025)

  1. Vessel diameter is very small
  2. Velocity of blood is very low
  3. Blood flows through a clogged vessel
  4. Blood viscosity increases
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Correct answer: (c) Blood flows through a clogged vessel

A deposit narrows the vessel and roughens it, so the speed rises past the critical value and the flow breaks up.

Bernoulli’s Effect and Blood Physics notes →

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