Ice has a density of 917 kg/m^3 and fresh water 1000 kg/m^3. What fraction of a floating ice block lies below the waterline?
A0.083
B1.09
C0.917
D0.500
Answer & Solution
Correct answer: C. 0.917
1. For a floating object the fraction submerged equals the object's average density divided by the fluid's density.
2. That ratio, taken against water, is the specific gravity of the object.
3. Substituting: fraction submerged = (917 kg/m^3) / (1000 kg/m^3).
4. This gives 0.917, so about 92 per cent of the ice sits below the surface.
5. The value 0.083 is the fraction showing above the water, which is the trap for answering the wrong half of the question.
6. The value 1.09 inverts the ratio, and a ratio above one would mean the block sinks rather than floats.
7. The value 0.500 assumes floating always means half submerged, which only holds when the object is exactly half as dense as the fluid.
_Source: OpenStax College Physics (CC BY 4.0), Ch 11 "Fluid Statics", section 11.7 Archimedes' Principle_
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