ASVAB (Armed Services Vocational Aptitude Battery)Mechanical Comprehension (MC)Medium
A small boat is floating on a lake. If the boat displaces 500 kg of water, what is the buoyant force acting on the boat?
- A5000 N
- B4900 N
- C500 N
- D9800 N
Show answer & explanationAnswer & explanation
Correct answer: B. 4900 N
According to Archimedes' Principle, the buoyant force (Fb) on a floating object is equal to the weight of the fluid displaced by the object. The weight of the displaced water is its mass (500 kg) multiplied by the acceleration due to gravity (g ≈ 9.8 m/s²). So, Fb = m_displaced_water × g = 500 kg × 9.8 m/s² = 4900 N.
Why the other options are wrong
- A. Incorrect, this would be if g was approximated as 10 m/s², which is often done for simpler calculations, but 9.8 m/s² is more precise.
- C. Incorrect, this is just the mass of the displaced water, not its weight.
- D. Incorrect, a multiplication error or used twice the mass.
Archimedes' Principle
States that the buoyant force on an object submerged or floating in a fluid is equal to the weight of the fluid displaced by the object.
- Applies to both fully submerged and floating objects.
- Buoyant force acts upwards.
- Explains why objects float or sink.
Memory trick: Archimedes found that displaced water's weight makes things float right.