The kilogram was originally fixed by reference to a definite volume of one substance. Which mass was chosen?
AThe mass of 1000 mL of water
BThe mass of 1000 mL of mercury
CThe mass of 100 mL of seawater
DThe mass of 100 mL of alcohol
Answer & Solution
Correct answer: A. The mass of 1000 mL of water
1. The metric system was set up so that water would have a density of 1 g per cubic centimetre.
2. A volume of 1000 mL is the same as 1000 cubic centimetres, so that much water has a mass of 1000 g.
3. The kilogram was therefore first devised as the mass of 1000 mL of water.
4. Mercury is 13.6 times denser than water, so 1000 mL of it would be far heavier than one kilogram.
_Source: OpenStax College Physics (CC BY 4.0), Ch 11 "Fluid Statics", section 11.2 Density_
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