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Difficulty: EasyBuoyancy and Archimedes' Principle

Two solid metal blocks, one made of aluminum and one made of lead, have the exact same size and shape. Both blocks are completely submerged in a tank of freshwater. Which of the following statements about the upward buoyant force acting on the blocks is true?

  1. The buoyant force is the same for both blocks because they displace the same volume of water.Answer
  2. B
    The buoyant force is greater on the lead block because it has a greater mass.
  3. C
    The buoyant force is greater on the aluminum block because it has less mass.
  4. D
    The buoyant force acting on each block is exactly equal to its respective weight.

Answer

The buoyant force is the same for both blocks because they displace the same volume of water.
According to Archimedes' Principle, buoyant force is determined entirely by the weight of the displaced fluid. Since both blocks have the exact same physical dimensions and are completely submerged in the same fluid, they displace the exact same volume of water. Therefore, they experience the exact same upward buoyant force, regardless of their individual weights or material compositions.

Step-by-Step Solution

1
Recall Archimedes' Principle.
The upward buoyant force exerted on a body immersed in a fluid is equal to the weight of the fluid that the body displaces.
This is the fundamental rule governing buoyancy.
2
Determine the displaced volume for each block.
Since both blocks have the exact same physical dimensions (size and shape) and are both completely submerged, they displace the exact same volume of water.
Displaced volume depends solely on the submerged volume of the object.
3
Compare the resulting buoyant forces.
Because they displace the same volume of the same fluid, the weight of the displaced fluid is identical for both blocks. Therefore, they experience the exact same buoyant force.
Buoyant force is independent of the object's mass, density, or weight, as long as the displaced volume is the same.

Key Concept

Archimedes' Principle (Volume vs. Mass)
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Topics

Buoyancy and Archimedes' Principle

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