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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

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1
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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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2
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A fluid flows in a horizontal pipe with a wide section and a narrow section.

How does the fluid flow speed compare between the two sections of pipe?

  • Fluid flow speed is the same in both sections of the pipe.

  • Fluid flow speed is greater in the wide section of the pipe.

  • Fluid flow speed is greater in the narrow section of the pipe.

  • Fluid flow speed does not depend on the width of the pipe.

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3
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A fluid flows in a horizontal pipe with two sections of different radius. The wide section has twice the radius of the narrow section.

What is the ratio of the fluid's speed in the narrow section of the pipe to its speed in the wide section?

  • 1:2

  • 1:4

  • 2:1

  • 4:1

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4
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A cylinder of mass 18 kg is at rest while partially submerged in a fluid of density 900 kg/m3.

Which of the following is most nearly the volume of the submerged section of the cylinder?

  • 0.020 cm3

  • 16 200 cm3

  • 0.020 m3

  • 16 200 m3

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5
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An open tank of depth 4 m contains a liquid of density 900 kg/m3. A small hole is drilled at the bottom of the tank.

Assuming atmospheric pressure at the surface and at the hole, which of the following is most nearly the speed of the liquid exiting the hole?

  • 6 m/s

  • 9 m/s

  • 13 m/s

  • 78 m/s

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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 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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3
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Two containers with scales; left shows liquid in container X, right shows container Y with submerged ball. Scales X and Y suggest measuring weight.

Two identical beakers, X and Y, are filled with water and placed on separate scales. The level of water in each beaker is equal when a wooden ball is placed in beaker Y, as shown in the figure.

Which of the following best describes the reading on scale Y?

  • The reading on scale Y is greater than the reading on scale X.

  • The reading on scale Y is less than the reading on scale X.

  • The readings on scale Y and scale X are the same.

  • There is not enough information to determine the reading on scale Y.

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4
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Two beakers rest on two scales, X and Y. Beaker X is filled with water. Beaker Y is filled with water to the same level as beaker Y, but contains a ball fully submerged. This ball is attached to the bottom of beaker Y via a string.

Two identical beakers, X and Y, are filled with water and placed on separate scales. The level of water in each beaker is equal when a wooden ball is immersed completely in beaker Y and attached by a taut string at the bottom, as shown in the figure.

Which of the following best describes the reading on scale Y?

  • The reading on scale Y is greater than the reading on scale X.

  • The reading on scale Y is less than the reading on scale X.

  • The readings on scale Y and scale X are the same.

  • There is not enough information to determine the reading on scale Y.

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5
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Diagram of a pipe with varying diameters showing cross-sectional areas (A_P), (A_Q), (A_R) and velocities (v_P), (v_Q), (v_R), indicating fluid flow.

An ideal fluid flows through a tube of varying cross-sectional area, as shown in the figure.

Which of the following ranks the fluid speeds v subscript P, v subscript Q, and v subscript R from least to greatest?

  • v subscript Q space less than space v subscript R space less than space v subscript P

  • v subscript P space equals space v subscript Q space equals space v subscript R

  • v subscript P space less than space v subscript Q space less than space v subscript R

  • v subscript P space less than space v subscript R space less than space v subscript Q

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1
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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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2
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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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3
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A boat floating on a lake carries a crate of density rho subscript c and volume V subscript c. The water in the lake has density rho subscript w. The crate is then thrown into the lake and sinks.

Which of the following correctly describes the change in the level of water in the lake?

  • The level rises by V subscript c open parentheses 1 space minus space rho subscript w over rho subscript c close parentheses

  • The level falls by V subscript c open parentheses 1 space minus space rho subscript w over rho subscript c close parentheses

  • The level falls by V subscript c open parentheses rho subscript c over rho subscript w space minus space 1 close parentheses

  • The level rises by V subscript c open parentheses rho subscript c over rho subscript w space minus space 1 close parentheses

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4
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A horizontal pipe carries water (density rho = 1000 kg/m3) at a flow rate of 0.02 m3/s. At a wide section of the pipe, the cross-sectional area is 0.05 m2. The pipe narrows to an area of 0.01 m2.

Assuming the flow is ideal, which of the following is most nearly the pressure difference between the wide and narrow sections of the pipe?

  • 1.6 Pa

  • 480 Pa

  • 950 Pa

  • 1900 Pa

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5
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A horizontal artery is shown with fluid flowing to the right. A section has fatty deposits at the top and bottom of the inside of the artery. Before this section is labelled as P_c. In between these deposits, at the same height as the previous point, is labelled P_f.

A build-up of fatty tissue over time can obstruct arteries, as shown in the figure.

Assuming the artery is horizontal when examined, how does the pressure in the region with fatty tissue P subscript f compare to the pressure in the clear region P subscript c?

  • P subscript c space less than space P subscript f

  • P subscript c space equals space P subscript f

  • P subscript c space greater than space P subscript f

  • There is not enough information to determine the pressure at each point.

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