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Fluid Statics and Dynamics MCQs — Physics

180 multiple-choice questions on Fluid Statics and Dynamics from Physics, each with the correct answer and, where available, a teacher's explanation. Read through them to revise the chapter, then practise the same questions one by one to test yourself.

1. As the temperature of a liquid rises, its viscosity usually:

  1. stays the same
  2. becomes infinite
  3. decreases
  4. increases

Answer: C) decreases

Explanation: Warm honey flows more easily. SLO P-11-B-41 · Understanding

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2. If the outlet area of a hose is reduced to one third, the speed of water leaving it becomes:

  1. one third
  2. unchanged
  3. 3 times as large
  4. 9 times as large

Answer: C) 3 times as large

Explanation: v propto 1/A. SLO P-11-B-37 · Understanding

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3. Ballast tanks in a submarine are filled with water to:

  1. increase the upthrust
  2. make it float higher
  3. reduce its weight
  4. increase its weight so it dives

Answer: D) increase its weight so it dives

Explanation: Pumping water out makes it rise. SLO P-11-B-34 · Application

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4. A fish has a streamlined shape to:

  1. increase drag
  2. float higher
  3. reduce drag in water
  4. increase its weight

Answer: C) reduce drag in water

Explanation: Less energy needed to swim. SLO P-11-B-42 · Understanding

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5. Squeezing a hose does NOT change:

  1. the mass of water leaving per second (for a steady supply)
  2. the shape of the jet
  3. the exit speed
  4. the range of the jet

Answer: A) the mass of water leaving per second (for a steady supply)

Explanation: Mass is conserved. SLO P-11-B-37 · Understanding

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6. Using Stokes' law, the drag on a sphere of radius 0.001 m moving at 0.1 m/s through a fluid of viscosity 0.001 Pa s is:

  1. 1.88 10^-6 N
  2. 9.42 10^-7 N
  3. 1 10^-7 N
  4. 3.77 10^-6 N

Answer: A) 1.88 10^-6 N

Explanation: F = 6pieta rv = 1.88 10^-6 N. SLO P-11-B-42 · Understanding

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7. Standing near the edge of a platform as a fast train passes is dangerous because:

  1. the platform vibrates
  2. the low pressure near the train can pull a person towards it
  3. the train pushes air into you
  4. the pressure becomes very high

Answer: B) the low pressure near the train can pull a person towards it

Explanation: Higher pressure behind pushes you in. SLO P-11-B-39 · Application

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8. For horizontal flow, Bernoulli's equation becomes:

  1. P = constant
  2. P + rho gh = constant
  3. P + 12rho v^2 = constant
  4. 12rho v^2 = rho gh

Answer: C) P + 12rho v^2 = constant

Explanation: h is the same everywhere. SLO P-11-B-40 · Application

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9. Smoke rising from a candle first flows smoothly then becomes irregular. The irregular part is:

  1. streamline flow
  2. steady flow
  3. turbulent flow
  4. laminar flow

Answer: C) turbulent flow

Explanation: Speed increases and eddies form. SLO P-11-B-35 · Knowledge

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10. Water is pumped up a vertical pipe of uniform area at steady speed. As it rises 10 m, its pressure (rho = 1000, g = 9.8):

  1. rises by 9.8 10^4 Pa
  2. stays the same
  3. falls by 9.8 10^4 Pa
  4. falls by 980 Pa

Answer: C) falls by 9.8 10^4 Pa

Explanation: Same speed (continuity), so Delta P = -rho gDelta h. SLO P-11-B-40 · Application

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11. Doubling the speed of a sphere in slow viscous flow (Stokes' law) makes the drag:

  1. four times
  2. double
  3. half
  4. unchanged

Answer: B) double

Explanation: F propto v. SLO P-11-B-42 · Understanding

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12. Superfluidity is observed in:

  1. molten iron
  2. water at room temperature
  3. liquid helium at very low temperatures
  4. honey

Answer: C) liquid helium at very low temperatures

Explanation: Helium-4 below about 2.17 K. SLO P-11-B-43 · Understanding

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13. Continuity is to fluid flow what Kirchhoff's current law is to circuits, because both express:

  1. Newton's second law
  2. conservation (of mass or charge) at a junction
  3. conservation of energy
  4. Ohm's law

Answer: B) conservation (of mass or charge) at a junction

Explanation: What flows in flows out. SLO P-11-B-38 · Application

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14. An incompressible fluid is one whose:

  1. temperature stays constant
  2. speed stays constant
  3. pressure is zero
  4. density stays constant

Answer: D) density stays constant

Explanation: Volume can't be squeezed. SLO P-11-B-35 · Knowledge

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15. The Plimsoll line on a ship shows:

  1. the ship's length
  2. the depth of the sea
  3. the speed of the ship
  4. the safe loading limit in different waters

Answer: D) the safe loading limit in different waters

Explanation: Marks for fresh/salt, summer/winter water. SLO P-11-B-34 · Application

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16. A superfluid is a liquid that:

  1. flows with zero viscosity
  2. is a solid
  3. has very high viscosity
  4. cannot flow

Answer: A) flows with zero viscosity

Explanation: No internal friction at all. SLO P-11-B-43 · Understanding

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17. Opening a parachute reduces terminal velocity because:

  1. upthrust disappears
  2. gravity is weaker
  3. the larger area greatly increases air drag
  4. weight decreases

Answer: C) the larger area greatly increases air drag

Explanation: A new, lower terminal speed is reached. SLO P-11-B-42 · Understanding

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18. Real fluids are viscous because:

  1. they have no molecules
  2. gravity acts on them
  3. intermolecular forces (and molecular collisions) resist layers sliding past each other
  4. they are incompressible

Answer: C) intermolecular forces (and molecular collisions) resist layers sliding past each other

Explanation: Layers drag on one another. SLO P-11-B-41 · Understanding

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19. Stokes' law for the drag on a small sphere moving slowly through a fluid is:

  1. F = eta rv^2
  2. F = 12rho v^2
  3. F = 6pieta r^2v
  4. F = 6pieta rv

Answer: D) F = 6pieta rv

Explanation: Valid for slow, laminar flow. SLO P-11-B-42 · Understanding

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20. A stone weighs 5.0 N in air and 3.0 N in water. Its density is:

  1. 1000 kg/m^3
  2. 2500 kg/m^3
  3. 1667 kg/m^3
  4. 600 kg/m^3

Answer: B) 2500 kg/m^3

Explanation: Relative density = 55 - 3 = 2.5. SLO P-11-B-33 · Application

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21. A ship stays upright (stable) if:

  1. it has no keel
  2. its centre of gravity is low and the centre of buoyancy shifts to give a restoring torque
  3. it carries no ballast
  4. its centre of gravity is very high

Answer: B) its centre of gravity is low and the centre of buoyancy shifts to give a restoring torque

Explanation: Heavy ballast is placed low. SLO P-11-B-34 · Application

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22. The SI unit of the coefficient of viscosity is:

  1. N/m
  2. kg/m^3
  3. J/s
  4. Pa s (or N s m^-2)

Answer: D) Pa s (or N s m^-2)

Explanation: Also written kg m^-1 s^-1. SLO P-11-B-41 · Understanding

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23. Which liquid is most viscous?

  1. honey
  2. water
  3. petrol
  4. alcohol

Answer: A) honey

Explanation: Honey flows very slowly. SLO P-11-B-41 · Understanding

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24. Water moves at 1 m/s in a pipe of diameter 4 cm, which narrows to 2 cm. The speed in the narrow part is:

  1. 8 m/s
  2. 5 m/s
  3. 2 m/s
  4. 4 m/s

Answer: D) 4 m/s

Explanation: v propto 1d^2: v2 = 1 ( 42 )^2 = 4 m/s. SLO P-11-B-36 · Application

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25. The physics principle behind squeezing a hose is:

  1. Hooke's law
  2. the equation of continuity
  3. Archimedes' principle
  4. Pascal's law only

Answer: B) the equation of continuity

Explanation: A1v1 = A2v2. SLO P-11-B-37 · Understanding

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