JAMB 2013 Physics · Question 28

A piece of cork floats in a liquid. What fraction of its volume will be immersed in the liquid? [Density of…

Question

A piece of cork floats in a liquid. What fraction of its volume will be immersed in the liquid? [Density of the cork = 0.25 x 103kgm-3, Density of the liquid = 1.25 x 103kgm-3]

A.0.8
B.0.5
C.0.2
D.0.1

Answer: C. 0.2

Explanation written with AI and checked against the answer key

Analyze the question: A cork floats in a liquid. We need the fraction of the cork's volume that is under the liquid surface. Concept: Law of flotation A floating body displaces a weight of liquid equal to its own weight. Weight of cork = Weight of liquid displaced ρ_cork × V_cork × g = ρ_liquid × V_immersed × g So the fraction immersed is: V_immersed / V_cork = ρ_cork / ρ_liquid Solution: Fraction = (0.25 × 10³) / (1.25 × 10³) Fraction = 0.25 / 1.25 = 1/5 = 0.2 Answer: The fraction immersed is 0.2, which is option C. Tip: For any floating object, the fraction submerged = density of object ÷ density of liquid. Since the cork is less dense than the liquid, the fraction must be less than 1. A quick check: 0.25 is one-fifth of 1.25, so the answer is 1/5 = 0.2. Don't pick 0.8 by mistake, which comes from inverting the ratio incorrectly or using the fraction that sticks out (1 − 0.2 = 0.8).

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