Two identical solid pieces, one of gold and other of silver, when immersed completely in water exhibit equal weights. When weighed in air (given that density of gold is greater than that of silver)
- A.the gold piece will weigh more
- B.the silver piece will weigh more
- C.both silver and gold pieces weigh equal
- D.weighing will depend on their masses
Correct answer
Explanation
The correct answer is B, the silver piece will weigh more. Silver is less dense, so a silver piece takes up more volume, loses more weight to buoyancy in water, and must therefore be heavier in air to show the same weight under water.
By Archimedes' principle, a body in water loses weight equal to the weight of the water it displaces, which depends on its volume. Weight in water equals weight in air minus this loss. Gold has a density of about 19.3 g/cm³ and silver about 10.5 g/cm³. If both pieces weighed the same in air, the silver one, being larger, would lose more and weigh less in water. For their weights in water to be equal, the silver piece must start with a greater weight in air.
Option A is wrong because the denser gold piece loses less to buoyancy, so it needs less weight in air. Option C is wrong because equal air weights would give unequal water weights. Option D is wrong because the condition of equal weights in water already fixes which piece is heavier.
Exam tip: loss of weight in water = weight of water displaced; the less dense body loses more.
Practice Questions
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- B.Martin Luther
- C.Johannes Kepler
- D.Copernicus
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- C.Urea is produced from digestion of starch.
- D.Urea is produced in lung and kidney.
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- B.Objective lens-Condenser-Body tube-Eyepiece
- C.Condenser-Objective lens-Body tube-Eyepiece
- D.Eyepiece-Objective lens-Body tube-Mirror
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- D.Haemoglobin is only used for blood clotting and not for carrying gases.
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- B.Histones are proteins that are present in nucleus in association with DNA.
- C.Histones are proteins associated with lipids in the cytosol.
- D.Histones are proteins associated with carbohydrates in the cytosol.
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