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Free Equation of Continuity MCQs with Answers

18 Equation of Continuity MCQs from Physics, each with the correct answer and a written explanation of why it is correct. Free and unlimited, with no account needed.

The equation of continuity expresses conservation of mass in fluid flow. For steady incompressible flow, Av remains constant, so fluid speed increases when the cross-sectional area decreases; for compressible flow, ρAv is constant. This relation describes flow rate and area-speed changes without including pressure effects from Bernoulli’s equation.

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18 questions

1. The equation of continuity for an incompressible fluid states that

Moderate
  • A. A1 v1 equals A2 v2, so the fluid speeds up where the pipe narrows
  • B. A1 v1 equals A2 v2, so the fluid slows down where the pipe narrows
  • C. the pressure is the same everywhere in the pipe
  • D. the density changes along the pipe

Explanation: The same volume passes every cross section each second, so where the area falls the speed must rise in proportion.

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Correct answer: A1 v1 equals A2 v2, so the fluid speeds up where the pipe narrows

2. Water flows through a pipe whose radius halves at a constriction. The speed of the water at the constriction becomes

  • A. half
  • B. double
  • C. four times
  • D. unchanged

Explanation: Area depends on the square of the radius, so halving the radius quarters the area, and by the continuity equation the speed must rise by a…

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Correct answer: four times

3. Water flows at 2 m per second through a pipe of cross sectional area 0.02 m squared. The volume flow rate is

Very hard
  • A. 0.04 cubic metres per second
  • B. 0.01 cubic metres per second
  • C. 4 cubic metres per second
  • D. 0.4 cubic metres per second

Explanation: Flow rate is area multiplied by speed, so 0.02 times 2 gives 0.04 cubic metres per second, that is 40 litres every second.

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Correct answer: 0.04 cubic metres per second

4. An incompressible fluid flows through a pipe that becomes narrower in one section. The fluid speed increases in that region to maintain:

Very hard
  • A. Constant pressure
  • B. Constant energy
  • C. Constant mass flow rate
  • D. Constant volume

Explanation: The same mass must pass every cross section each second, so where the area falls the speed must rise in proportion, which is the equation…

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Correct answer: Constant mass flow rate

5. The equation of continuity is obtained by applying in the law of conservation of_____________?

  • A. Mass
  • B. Energy
  • C. Momentum
  • D. All

Explanation: The continuity equation comes from conservation of mass: the mass entering a pipe per second equals the mass leaving it per second.

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Correct answer: Mass

6. According to equation of continuity A1V1 = A2V2 = constant. The constant is equal to_______________?

  • A. Flow rate
  • B. Volume of fluid
  • C. Mass of fluid
  • D. The density of the fluid

Explanation: In A1V1 = A2V2, area in m² multiplied by speed in m/s gives m³/s, which is volume flow rate or discharge.

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Correct answer: Flow rate

7. In a cement factory, a viscous liquid flows through a pipe with an area of cross-section 6 m2 at a velocity of 8 m/s.When this fluid moves forward, the area of cross-section of the pipe decreases to 4 m2 The velocity of the liquid will now be

  • A. 3 m/s.
  • B. 12 m/s.
  • C. 18 m/s.
  • D. 24 m/s.

Explanation: The principle of continuity for incompressible fluid flow states that the product of the cross-sectional area and velocity must remain…

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Correct answer: 12 m/s.

8. The equation of continuity of a fluid is related to the conservation of

  • A. Mass
  • B. Energy
  • C. Momentum
  • D. Angular momentum.

Explanation: The equation of continuity expresses the conservation of mass in fluid dynamics.

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Correct answer: Mass

9. In a cement factory, a viscous liquid flows through a pipe with an area of cross-section 6 m² at a velocity of 8 m/s.When this fluid moves forward, the area of cross-section of the pipe decre velocity of the liquid will now be 4 m² The

  • A. 3 m/s.
  • B. 12 m/s.
  • C. 18 m/s.
  • D. 24 m/s.

Explanation: The principle of conservation of mass for a fluid in a closed system is given by the equation: A1 * V1 = A2 * V2, where A1 and V1 are the…

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Correct answer: 12 m/s.

10. According to the equation of continuity, if the cross-sectional area of a pipe decreases, then the speed of the fluid passing through it

  • A. Increases
  • B. Decreases
  • C. Remains the same
  • D. Varies unpredictably

Explanation: The equation of continuity states that the mass flow rate must be constant in a closed system.

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Correct answer: Increases

11. In a fire fighting machine, a jet is attached to the head of water pipes to increase the

  • A. Mass of water flowing out of it.
  • B. Volume of water flowing out of it.
  • C. Velocity of water flowing out of it.
  • D. Distance covered by water flowing out of it.

Explanation: The correct answer is Option C: The jet is designed to increase the velocity of water flowing out of it.

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Correct answer: Velocity of water flowing out of it.

12. An industrial liquid flows through a section of a pipe with an area of cross-section 2 m2 at a velocity of 10 m/s. If at a certain section the area of cross-section decreases to 1 m2, then the velocity of the liquid will be

  • A. 5 m/s
  • B. 10 m/s
  • C. 15 m/s
  • D. 20 m/s

Explanation: According to the principle of continuity for fluid flow, the product of the cross-sectional area and velocity of a fluid must remain…

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Correct answer: 20 m/s

13. In a cement factory, a viscous liquid flows through a pipe with an area of cross-section 6 m2at a velocity of 8 m/s. When this fluid moves forward, the area of cross-section of the pipe decreases to 4 m2 The velocity of the liquid will now be

  • A. 12 m/s.
  • B. 3 m/s.
  • C. 18 m/s.
  • D. 24 m/s.

Explanation: To solve this problem, use the principle of continuity, which states that the product of the cross-sectional area and velocity of a fluid…

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Correct answer: 12 m/s.

14. A rocket is made to travel at a high speed by making the ejection nozzle narrow. This phenomenon is based on

  • A. Turbulent flow.
  • B. Terminal velocity.
  • C. Torricelli's theorem.
  • D. Equation of continuity.

Explanation: The correct answer is the equation of continuity. This principle of fluid dynamics explains that as a fluid flows through a pipe, if the…

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Correct answer: Equation of continuity.

15. A pipe varies uniformly in diameter from 2m to 4m. An incompressible fluid enters the pipe with velocity 16 m/s. What is velocity of fluid when it leaves the pipe?

  • A. 64 m/s
  • B. 32 m/s
  • C. 8 m/s
  • D. 4 m/s

Explanation: Given that,d1=2md2=4mV1=16m/sV2=𝑥From flow rate,A1V1 =A2V2(πr2)1V1=(πr2)2V2(d12/4)V1=(d22/4)V2By substituting the given values,𝑥= V2 =…

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Correct answer: 4 m/s

16. Conservation of mass of fluid flow leads to:

  • A. Bernoulli's equation
  • B. Venturi meter
  • C. Equation of motion
  • D. Equation of continuity

Explanation: The correct answer is D) Equation of continuity, as it directly expresses the conservation of mass in fluid flow.

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Correct answer: Equation of continuity

17. An Incompressible liquid flow along the pipe with area of cross section A1 and A2 with velocities V1 and V2 respectively. The ratio of the speeds V1 / V2 is:

  • A. A1/A2
  • B. A2/A1
  • C. (A1 + A2)/(V1 + V2)
  • D. (V1 + V2)/(A1 + A2)

Explanation: According to the continuity equation for incompressible fluids, the flow rate (product of cross-sectional area and velocity) is constant.

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Correct answer: A2/A1

18. Water flows from a 6.0cm diameter pipe into 8.0cm diameter pipe. The speed in the 6.0cm pipe is 5.0m/s. the speed in the 8cm pipe is:

  • A. 2.8m/s
  • B. 3.7m/s
  • C. 6.6m/s
  • D. 8.8m/s

Explanation: The problem can be solved using the continuity equation, which states that A1V1 = A2V2, where A is the cross-sectional area of the pipe.

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Correct answer: 2.8m/s
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