Answer: Falls (iron displaced less water when submerged than when floating).
- A Falls (iron displaced less water when submerged than when floating)
- B Rises, since the total mass of boat plus cubes hasn't changed
- C Stays exactly the same regardless of how the cubes are distributed
- D Depends only on the density of iron relative to the boat's hull
Correct answer: A. Falls (iron displaced less water when submerged than when floating)
Explanation: When iron is on the boat, it displaces water equal to its weight (dense iron displaces a lot). When submerged, it displaces only its own volume (much less). So water level falls.
Since the same volume of fluid must pass every cross-section per second (continuity), the fluid speeds up where the pipe narrows; Bernoulli's equation then says this faster-moving fluid has lower pressure - the principle behind a venturi meter and an aircraft wing's lift.
Concept context
Pressure, buoyancy, Bernoulli equation, viscosity, and surface tension.