A body sinks in water when
- A.density of water is greater than density of body
- B.density of water is less than density of body
- C.density of water is equal to density of body
- D.the body is heavy
Correct answer
Explanation
The correct answer is B, density of water is less than density of body. A body sinks when its weight is greater than the buoyant force of the water it displaces, which happens when it is denser than water.
By Archimedes' principle, a fully submerged body is pushed up by a force equal to the weight of water it displaces. For the same volume, a body denser than water weighs more than that displaced water, so the net force is downward and it sinks. Water has a density of about 1 g/cm³; iron (about 7.9 g/cm³) sinks, while wood and ice float.
A is wrong because a body less dense than water floats.
C is wrong because equal densities make the body stay suspended wherever it is placed, neither rising nor sinking.
D is wrong because weight alone does not decide sinking: a heavy steel ship floats because its hollow shape lowers its average density.
Exam tip: denser than the liquid, it sinks; less dense, it floats; equal, it stays suspended.
Practice Questions
View allBronze is an alloy of copper and
- A.nickel
- B.iron
- C.tin
- D.aluminium
Show answer
Bronze is an alloy of copper and tin, usually about 88 parts copper to 12 parts tin. Adding tin makes copper harder, stronger and easier to cast, and bronze also resists corrosion well.
Read the full explanation →Which one of the following instruments is used for measuring moisture content of air?
- A.Hydrometer
- B.Hygrometer
- C.Hypsometer
- D.Pycnometer
Show answer
A hygrometer measures humidity, that is, the amount of water vapour or moisture in the air. The name comes from the Greek "hygros", meaning wet.
Read the full explanation →Which one of the following elements is present in the green pigment of leaves?
- A.Magnesium
- B.Iron
- C.Calcium
- D.Copper
Show answer
The green pigment of leaves is chlorophyll, and a magnesium atom sits at the centre of every chlorophyll molecule.
Read the full explanation →Consider the following actions :
1. Detection of car crash/collision which results in the deployment of airbags almost instantaneously
2. Detection of accidental free fall of a laptop towards the ground which results in the immediate turning off of the hard drive
3. Detection of the tilt of the smartphone which results in the rotation of display between portrait and landscape mode
In how many of the above actions is the function of accelerometer required?
- A.Only one
- B.Only two
- C.All three
- D.None
Show answer
An accelerometer measures acceleration, including the pull of gravity, and each of the three actions depends on reading it. An accelerometer is a small sensor, today usually a MEMS (micro-electro-mechanical system) chip, that senses changes in speed and the direction of gravity.
Read the full explanation →Consider the following statements :
1. Carbon fibres are used in the manufacture of components used in automobiles and aircrafts.
2. Carbon fibres once used cannot be recycled.
Which of the statements given above is/are correct?
- A.1 only
- B.2 only
- C.Both 1 and 2
- D.Neither 1 nor 2
Show answer
Carbon fibre is widely used in cars and aircraft for its strength and low weight, and it can be recovered and recycled.
Read the full explanation →