AP Physics 1 — Unit 8: Fluids
Practice questions, answers, and key terms for Unit 8, aligned to the College Board CED.
AP Physics 1 Unit 8 practice questions
Two metal cubes are made of the same alloy, but one is twice the size of the other. You weigh and measure both. What single property comes out identical for both cubes?
Density — ρ = m/V, the same for any size of the alloy. Mass and volume both scale, so the ratio holds.
You squeeze a sealed water balloon hard and the shape changes but the volume barely budges. You do the same to a sealed bag of air and it compresses easily. What property of water makes it model-able as an ideal fluid?
Water is treated as incompressible; volume holds steady. An ideal fluid is incompressible with no viscosity.
A wooden sphere (density 660 kg/m³) floats in water (1000 kg/m³). What fraction of its volume sits below the surface, and what sets that fraction?
66% is submerged, the ratio of object to fluid density (660/1000). Shape is irrelevant; only the density ratio sets it.
A solid steel ball sinks in water but a hollow steel ship floats. Same metal, opposite outcomes. What actually decides whether something sinks?
Average density relative to the fluid decides whether it sinks. The hollow ship encloses air, dropping its density below water's.
A diver descends to 10 m in a lake, then later swims to 10 m down in the ocean. Same depth, different fluids. Which gauge pressure formula tells you what changed?
P_gauge = ρgh — denser water raises it at equal depth. Density rides along in the formula, not just depth.
A skinny test tube and a wide bucket are both filled with water to exactly 30 cm deep. A pressure sensor sits at the bottom of each. Which sensor reads higher pressure?
Neither — both read the same, since pressure depends on depth. P = P₀ + ρgh ignores container width and volume.
At the surface of a pool the pressure on your skin is atmospheric. Two meters down it's clearly more. What equation links the deeper pressure to the surface pressure?
P = P₀ + ρgh — surface pressure plus the column's gauge term. Don't drop the P₀ term.
You push a thumbtack into a wall: tiny point goes in easily, flat head doesn't. Same force from your thumb on both ends. What quantity explains why only the sharp end pierces?
Pressure, P = F/A — same force on a tiny area spikes. Spread over the flat head, it gives little.
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Key terms in Unit 8
These 12 terms show up in the Unit 8 cards. Each one links to its definition in the AP Physics 1 key-term reference.
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