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AP Physics 1: Fluids — Practice Questions & Answers
Density, pressure with depth, buoyancy, Pascal's principle, continuity, and Bernoulli's equation for ideal fluid flow.
210 practice questions available for this unit — here are 10 with full answers and explanations.
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Practice questions with answers
1
Multiple choice · Easy
Which expression correctly defines the density of a substance?
mass divided by volume
volume divided by mass
mass times volume
force divided by area
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Why Density is mass per unit volume, rho = m / V, with SI units of kg/m^3.
2
Multiple choice · Easy
Pressure is defined as the magnitude of the force exerted perpendicular to a surface divided by which quantity?
the area of the surface
the volume of the fluid
the length of the surface
the mass of the object
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Why Pressure P = F / A, where F is the perpendicular force and A is the area over which it acts. The SI unit is the pascal (Pa = N/m^2).
3
Multiple choice · Easy
A solid object is fully submerged in water. According to Archimedes' principle, the buoyant force on the object equals which of the following?
the weight of the fluid displaced by the object
the weight of the object itself
the mass of the object times its volume
the atmospheric pressure times the object's area
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Why Archimedes' principle states the buoyant force equals the weight of the fluid displaced by the object, F_b = rho_fluid * V_displaced * g.
4
Multiple choice · Easy
As you descend deeper into a lake, the pressure exerted by the water on you does what?
increases
decreases
stays exactly the same
becomes zero
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Why Gauge pressure in a static fluid increases with depth as P = rho * g * h, so deeper means greater pressure.
5
Fill in the blank · Easy
The SI unit of pressure, equal to one newton per square meter, is called the
Check answer
Answer:
pascal / Pa
Why One pascal (Pa) is defined as 1 N/m^2.
6
Fill in the blank · Easy
An object floats in a fluid when the upward
Check answer
Answer:
buoyant / buoyancy
Why For floating equilibrium, the buoyant force equals the object's weight.
7
Multiple choice · Medium
A cube of metal has a mass of 2.4 kg and a side length of 0.10 m. What is its density?
2400 kg/m^3
240 kg/m^3
24000 kg/m^3
24 kg/m^3
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Why Volume = (0.10)^3 = 1.0e-3 m^3, so rho = 2.4 / 1.0e-3 = 2400 kg/m^3.
8
Multiple choice · Medium
What is the gauge pressure at a depth of 5.0 m below the surface of fresh water (rho = 1000 kg/m^3, g = 10 m/s^2)?
50000 Pa
5000 Pa
500000 Pa
2000 Pa
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Why P = rho * g * h = 1000 * 10 * 5.0 = 50000 Pa.
9
Multiple choice · Medium
A hydraulic lift has a small piston of area 0.0050 m^2 and a large piston of area 0.50 m^2. If a force of 100 N is applied to the small piston, what force is exerted by the large piston?
10000 N
1000 N
100 N
1.0 N
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Why By Pascal's principle the pressure is equal: F2 = F1 * (A2/A1) = 100 * (0.50/0.0050) = 10000 N.
10
Multiple choice · Medium
Water flows through a horizontal pipe that narrows from a cross-sectional area of 0.040 m^2 to 0.010 m^2. If the speed in the wide section is 2.0 m/s, what is the speed in the narrow section?
8.0 m/s
0.50 m/s
4.0 m/s
2.0 m/s
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Why By continuity A1 v1 = A2 v2: v2 = (0.040 * 2.0) / 0.010 = 8.0 m/s.
Key terms in Fluids
Fluid: A substance that flows and takes the shape of its container, including both liquids and gases.
Density: The mass of a substance per unit volume, indicating how tightly matter is packed together.
Mass density formula: Density equals mass divided by volume (rho = m/V), measured in kg/m^3.
Volume: The amount of three-dimensional space that a substance or object occupies, measured in m^3.
Specific gravity: The ratio of a substance's density to the density of water, a dimensionless comparison value.
Density of water: The standard reference density of liquid water, approximately 1000 kg/m^3.
Pressure: The amount of force applied perpendicular to a surface divided by the area of that surface.
Pressure formula: Pressure equals force divided by area (P = F/A), measured in pascals.
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