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Fluid Statics and Dynamics MCQs — Physics (page 2)

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.

26. The layer of a viscous fluid in contact with a pipe wall is:

  1. moving fastest
  2. turbulent always
  3. at rest (no-slip condition)
  4. moving at the average speed

Answer: C) at rest (no-slip condition)

Explanation: It sticks to the wall. SLO P-11-B-41 · Understanding

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27. The ideal-fluid assumption used for the squeezed hose is that water is:

  1. turbulent
  2. compressible
  3. incompressible
  4. very viscous

Answer: C) incompressible

Explanation: Its density stays the same. SLO P-11-B-37 · Understanding

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28. Where a pipe narrows, the speed of an ideal fluid:

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

Answer: B) increases

Explanation: Smaller A needs larger v. SLO P-11-B-36 · Application

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29. A stone weighs 5.0 N in air and 3.0 N fully in water. The upthrust is:

  1. 8.0 N
  2. 2.0 N
  3. 3.0 N
  4. 5.0 N

Answer: B) 2.0 N

Explanation: Apparent loss of weight = upthrust. SLO P-11-B-33 · Application

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30. A floating ice cube melts in a glass of water. The water level:

  1. stays the same
  2. first rises then falls
  3. falls
  4. rises

Answer: A) stays the same

Explanation: The ice displaced exactly its own mass of water. SLO P-11-B-33 · Application

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31. At terminal velocity the kinetic energy of a falling body:

  1. stays constant
  2. decreases
  3. increases
  4. is zero

Answer: A) stays constant

Explanation: Speed is constant. SLO P-11-B-42 · Understanding

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32. The equation of continuity for an ideal fluid is:

  1. v1A1 = v2A2
  2. A1v2 = A2v1
  3. A1v1 = A2v2
  4. P1A1 = P2A2

Answer: C) A1v1 = A2v2

Explanation: Volume flow rate is constant. SLO P-11-B-36 · Application

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33. A body floats when:

  1. it is denser than the fluid
  2. its weight is greater than the upthrust
  3. its weight equals the upthrust on it
  4. it has no weight

Answer: C) its weight equals the upthrust on it

Explanation: Law of flotation. SLO P-11-B-33 · Application

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34. The equation of continuity is a statement of conservation of:

  1. energy
  2. momentum
  3. charge
  4. mass

Answer: D) mass

Explanation: Mass entering = mass leaving per second. SLO P-11-B-38 · Application

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35. The temperature below which helium-4 becomes superfluid is about:

  1. 273 K
  2. 77 K
  3. 2.17 K
  4. 100 K

Answer: C) 2.17 K

Explanation: Called the lambda point. SLO P-11-B-43 · Understanding

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36. In a time Delta t, the mass of fluid passing a cross-section of area A at speed v is:

  1. AvDelta t
  2. rho ADelta t
  3. rho vDelta t
  4. rho AvDelta t

Answer: D) rho AvDelta t

Explanation: Volume = A vDelta t. SLO P-11-B-38 · Application

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37. A ping-pong ball can be held in a stream of air from a hair dryer because:

  1. it has no weight
  2. the air pushes it from below only
  3. it is magnetic
  4. the fast air around it has lower pressure, pulling it back into the stream

Answer: D) the fast air around it has lower pressure, pulling it back into the stream

Explanation: Bernoulli effect keeps it centred. SLO P-11-B-39 · Application

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38. Covering part of a tap outlet with your thumb makes the water spray because:

  1. it reduces the water pressure in the pipe to zero
  2. water becomes compressible
  3. it cools the water
  4. the reduced area increases the water's speed

Answer: D) the reduced area increases the water's speed

Explanation: Continuity again. SLO P-11-B-37 · Understanding

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39. Water flows at 0.5 m/s through a pipe section of area 10 m^2 into a section of area 2 m^2. Its speed there is:

  1. 5 m/s
  2. 1.25 m/s
  3. 2.5 m/s
  4. 0.1 m/s

Answer: C) 2.5 m/s

Explanation: A1v1 = A2v2 Rightarrow v2 = 10 0.52 = 2.5 m/s. SLO P-11-B-36 · Application

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40. A fluid of density 1000 kg/m^3 flows at 2 m/s through a pipe of area 0.01 m^2. The mass flow rate is:

  1. 40 kg/s
  2. 200 kg/s
  3. 20 kg/s
  4. 2 kg/s

Answer: C) 20 kg/s

Explanation: Mass flow rate = rho A v = 20 kg/s. SLO P-11-B-38 · Application

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41. A submarine floating fully submerged at constant depth has:

  1. weight equal to the upthrust
  2. zero upthrust
  3. weight greater than the upthrust
  4. zero weight

Answer: A) weight equal to the upthrust

Explanation: Neutral buoyancy. SLO P-11-B-34 · Application

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42. Water leaks through a small hole 20 m below the surface of an open tank. The speed of efflux is (g = 9.8):

  1. 28 m/s
  2. 9.9 m/s
  3. 39.6 m/s
  4. 19.8 m/s

Answer: D) 19.8 m/s

Explanation: Torricelli's theorem (from Bernoulli): v = 2gh = 2(9.8)(20) = 19.8 m/s. SLO P-11-B-40 · Application

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43. Water (rho = 1000 kg/m^3) flows horizontally. At one point P = 1.5 10^5 Pa and v = 1 m/s; at another v = 4 m/s. The pressure there is:

  1. 2.85 10^5 Pa
  2. 1.43 10^5 Pa
  3. 71,200 Pa
  4. 1.43 10^6 Pa

Answer: B) 1.43 10^5 Pa

Explanation: P2 = P1 + 12rho(v1^2 - v2^2) = 1.5 10^5 + 500(1 - 16) = 1.43 10^5 Pa. SLO P-11-B-40 · Application

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44. The terminal velocity of a sphere in a viscous fluid (Stokes' regime) is proportional to:

  1. r^3
  2. 1r
  3. r^2
  4. r

Answer: C) r^2

Explanation: vt = 2r^2(rho - sigma)g9eta. SLO P-11-B-42 · Understanding

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45. Laminar flow means the fluid moves in:

  1. circles only
  2. pulses
  3. random eddies
  4. smooth layers sliding past each other

Answer: D) smooth layers sliding past each other

Explanation: Lamina = thin layer. SLO P-11-B-35 · Knowledge

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46. Thick syrup takes longer than water to pour out of a bottle because:

  1. its density is lower
  2. it has no weight
  3. its viscosity is much higher
  4. it is compressible

Answer: C) its viscosity is much higher

Explanation: Greater internal friction. SLO P-11-B-41 · Understanding

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47. During a storm, roofs can be lifted off because:

  1. air inside cools
  2. fast wind above the roof lowers the pressure there
  3. the wind pushes down on the roof
  4. rain makes it lighter

Answer: B) fast wind above the roof lowers the pressure there

Explanation: Higher pressure inside pushes up. SLO P-11-B-39 · Application

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48. Bernoulli's equation for an ideal fluid along a streamline is:

  1. A1v1 = A2v2
  2. PV = constant
  3. P + rho v + rho gh = constant
  4. P + 12rho v^2 + rho gh = constant

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

Explanation: Pressure energy + KE + PE per unit volume. SLO P-11-B-40 · Application

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49. Viscous drag on a moving object depends on:

  1. nothing
  2. its speed, size and shape and the fluid's viscosity
  3. its colour only
  4. its temperature only

Answer: B) its speed, size and shape and the fluid's viscosity

Explanation: e.g. Stokes' law. SLO P-11-B-42 · Understanding

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50. 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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