If some object is weighed when submerged in water, what will happen to its weight compared to its weight in air ?
- A.Increase
- B.Decrease
- C.Remain exactly the same
- D.Increase or decrease cannot be predicted
Correct answer
Explanation
The correct answer is B, Decrease. When an object is weighed under water, the water pushes up on it with a buoyant force, so it seems lighter than in air; this reduced reading is its apparent weight.
By Archimedes' principle, a body wholly or partly immersed in a fluid feels an upward force equal to the weight of the fluid it displaces. Its apparent weight in water is therefore its true weight minus the weight of the water displaced. The loss in weight is used to find the relative density of a solid: weight in air divided by loss of weight in water. The object's mass and its true weight do not change; only the reading on the spring balance falls. This is also why lifting a heavy stone feels easier while it is still under water.
A is wrong: buoyancy acts upward, so the reading cannot go up. C is wrong: the reading stays the same only in a vacuum-like case with no fluid to push up. D is wrong: the result can be predicted; it always decreases.
Exam tip: apparent weight = true weight − weight of fluid displaced; relative density = weight in air ÷ loss of weight in water.
Practice Questions
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- B.Martin Luther
- C.Johannes Kepler
- D.Copernicus
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- D.Urea is produced in lung and kidney.
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- B.Objective lens-Condenser-Body tube-Eyepiece
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- 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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