A body weighing 14N in air is partially immersed in water. If the mass of water displaced in the process is…

Analyze the question: The body is partially immersed in water, and we're told the mass of water displaced. We need the upthrust (buoyant force) on the body.

Concept (Archimedes' Principle): The upthrust on a body in a fluid equals the weight of the fluid displaced.

Upthrust = mass of fluid displaced × g

The 14 N weight of the body in air is extra information here (a distractor). It isn't needed to find the upthrust.

Solution:

1. Mass of water displaced = 200 g = 0.2 kg (divide by 1000 to convert to kg)
2. Weight of water displaced = mg = 0.2 × 10 = 2.0 N
3. Upthrust = weight of water displaced = 2.0 N

Check: The apparent weight in water would be 14 − 2 = 12 N, which is reasonable because the upthrust is less than the body's weight.

The answer is A. 2.0 N.

Exam tip: Always convert grams to kilograms before using F = mg. Also remember that "upthrust = weight of fluid displaced" doesn't depend on the body's own weight. WASSCE often includes such extra data to test whether you understand the principle.