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AP®PhysicsCollege BoardPhysics 1: Algebra-BasedExam QuestionsUnit 8: FluidsFluid Mechanics

Fluid Mechanics (College Board AP® Physics 1: Algebra-Based)

Exam Questions

5 mins5 questions
1
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Two cubes, A and B, of equal volume V are placed on the surface of a container of water. Cube A is observed to sink while cube B is observed to float, but is partially submerged.

Which of the following statements is false?

  • Cube A displaces a greater volume of water than cube B.

  • The weight of cube A is greater than the weight of the water it displaces.

  • A volume V of displaced water has the same weight as cube B.

  • The buoyant force on A is greater than the buoyant force on B.

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2
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A funnel-shaped mouthpiece leads horizontally to a tubular chamber. This chamber then branches into two tubes. One is narrower and one is thicker. The thicker tube leads to a cylindrical flask of water, via a 90 degree bend downwards. The water level in the thicker tube is at a level X. The narrower tube also leads to the cylindrical flask via a 90 degree bend downwards. It then widens to the same radius as tube X before reaching the conical flask. The level Y of the water in this tube is unknown.

The classroom equipment shown in the figure is used to demonstrate fluid mechanics to students. The user blows into the mouthpiece and observes the levels reached by water in the two tubes, X and Y.

How do the levels X and Y compare?

  • Levels X and Y are equal because the pressure of a fluid depends on height only, not container shape.

  • Level Y is higher than level X because air speed is higher in tube Y so air pressure is greater.

  • Level X is higher than level Y because air speed is higher in tube X so air pressure is lower.

  • Level X is lower than level Y because air speed is higher in tube Y so air pressure is lower.

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3
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A marble suspended from a string is fully submerged in water. It experiences an upward force of F. When the same marble is submerged in oil, it experiences an upward force of 5 over 6 F.

Which of the following is most nearly the density of the oil?

  • 500 kg/m3

  • 700 kg/m3

  • 800 kg/m3

  • 900 kg/m3

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4
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A section of cylindrical pipe carries water vertically downwards. The upper section of the pipe has a cross-sectional area of 4.5 m2 and water flows in the lower section of the pipe at a velocity of 12 m/s. The water pressure in the upper section of the pipe is 1.3 × 105 Pa, and the water pressure in the lower section of the pipe is 1.5 × 105 Pa.

If the volumetric flow rate of water through the pipe is 36 m3/s, which of the following is most nearly the total length of the pipe?

  • 2.0 m

  • 4.4 m

  • 5.6 m

  • 6.0 m

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5
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A trumpet held horizontally is blown and air leaves it at a speed v. The mouthpiece of the trumpet has a radius equal to one third of the widest part at the far end.

Which of the following expressions correctly describes the pressure of air at the mouthpiece?

  • 100 space 000 space minus space 40 rho v squared

  • 4 rho v squared

  • 100 space 000 space minus space 4 rho v squared

  • 100 space 000 space plus space 4 rho v squared

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