Whether an object will float or sink in a liquid, depends on
- A.mass of the object only
- B.mass of the object and density of liquid only
- C.difference in the densities of the object and liquid
- D.mass and shape of the object only
Correct answer
Explanation
The correct answer is C, difference in the densities of the object and liquid. An object denser than the liquid sinks, and one less dense than the liquid floats.
By Archimedes' principle, a body placed in a liquid feels an upward buoyant force equal to the weight of the liquid it displaces. If the body's average density is less than that of the liquid, it can displace its own weight of liquid before it is fully under, so it floats. If its density is greater, even full immersion displaces less than its weight, so it sinks. This is why a heavy steel ship floats: its hollow hull gives it a low average density. The same idea explains why an egg sinks in fresh water but floats in salty water.
A is wrong: a large log floats while a tiny pebble sinks, so mass alone does not decide.
B is wrong: the object's mass alone is not enough; its volume, and so its density, matters.
D is wrong: the liquid matters too; the same object can float in one liquid and sink in another.
Exam tip: density of object less than liquid means it floats; relative density below 1 floats in water.
Practice Questions
View allThe speed of the wind is measured by
- A.wind vane
- B.wind rose
- C.barometer
- D.anemometer
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An anemometer measures how fast the wind is blowing; its name comes from the Greek word anemos, meaning wind.
Read the full explanation →Brilliance of diamond is due to
- A.interference of light
- B.diffraction of light
- C.polarization of light
- D.total internal reflection of light
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Light that enters a cut diamond is reflected again and again inside it before it escapes, which makes the stone sparkle.
Read the full explanation →Which one of the following is NOT an electromagnetic wave ?
- A.Light wave
- B.Radio wave
- C.Sound wave
- D.Micro wave
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Sound is a mechanical wave that needs a medium to travel, while the other three are electromagnetic waves. Sound travels as a longitudinal wave of compressions and rarefactions in air, water or solids, which is why it cannot pass through a vacuum.
Read the full explanation →Which one of the following is NOT true for an electromagnetic wave ?
- A.Electromagnetic wave transports energy and momentum
- B.Electromagnetic wave can be polarized and reflected
- C.Electromagnetic wave is longitudinal
- D.Electromagnetic wave propagation is described by the varying electric and magnetic fields
Show answer
Electromagnetic waves are transverse, not longitudinal, so this statement is false. In an electromagnetic wave the electric field and the magnetic field oscillate at right angles to each other and both at right angles to the direction in which the wave travels.
Read the full explanation →Which one of the following frequency ranges is sensitive to human ears ?
- A.0-200 Hz
- B.20-20,000 Hz
- C.200-20,000 Hz only
- D.2,000-20,000 Hz only
Show answer
The normal human ear hears sound from about 20 hertz to 20,000 hertz, the audible range. Frequency, measured in hertz, is the number of vibrations per second, and it decides the pitch of a sound: the higher the frequency, the shriller the note.
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