AP Physics AP Physics Fluid Mechanics & Energy Systems 1 — Questions and Answers
Question 1: Pressure in a static fluid at depth h is given by:
- P = ρgh²
- P = ρg/h
- P = ρgh (Correct answer)
- P = ρh
Correct answer: P = ρgh
Hydrostatic pressure at depth h in a fluid of density ρ is P = ρgh.
Question 2: Archimedes' principle states that the buoyant force on an object equals:
- The weight of the object
- The density of the object times volume
- The weight of displaced fluid (Correct answer)
- The pressure times the object's surface area
Correct answer: The weight of displaced fluid
Archimedes' principle states that the buoyant force equals the weight of the fluid displaced by the object.
Question 3: According to the continuity equation for an incompressible fluid, if pipe area decreases, fluid speed:
- Decreases
- Stays the same
- Increases (Correct answer)
- Becomes zero
Correct answer: Increases
The continuity equation A₁v₁ = A₂v₂ requires speed to increase when cross-sectional area decreases.
Question 4: Bernoulli's equation relates pressure, fluid speed, and height for:
- Compressible, viscous flow
- Incompressible, non-viscous steady flow (Correct answer)
- Turbulent flow only
- Gases only
Correct answer: Incompressible, non-viscous steady flow
Bernoulli's equation applies to incompressible, non-viscous fluids in steady (laminar) flow.
Question 5: In Bernoulli's equation, where fluid speed is greatest, the pressure is:
- Greatest
- Lowest (Correct answer)
- Unchanged
- Equal to atmospheric
Correct answer: Lowest
Bernoulli's equation shows that increased fluid speed corresponds to decreased pressure.
Question 6: A fluid of density 1000 kg/m³ flows through a pipe. If the cross-sectional area drops from 0.04 m² to 0.01 m² and initial speed is 2 m/s, what is the new speed?
- 0.5 m/s
- 2 m/s
- 8 m/s (Correct answer)
- 4 m/s
Correct answer: 8 m/s
By continuity: v₂ = A₁v₁/A₂ = (0.04 × 2)/0.01 = 8 m/s.
AP Physics AP Physics Fluid Mechanics & Energy Systems 1
Pressure in a static fluid at depth h is given by: