Question

Which statement is correct ?
a) Mass is a gravitational force but weight is not a gravitational force
b) Mass is not a gravitational force and weight is not a gravitational force
c) The unit of mass is kilogram and the unit of weight is Newton.
d) The unit of mass is Newton and the unit of weight is kilogram

Answer 1

Hint: Mass and the weight of a body are not independent quantities. Mass of a body is a fundamental quantity whereas the weight of the same body is the derived quantity. Hence defining mass of a body in terms of its weight will allow us to select the correct alternative from those provided.
Formula used:
${{F}_{G}}=mg$

Complete answer:
Mass of the body is the amount of matter that a body has. To understand this more precisely mass is the amount of atoms that a body has within its defined volume. Weight is the force by which the gravity of a planet pulls the mass towards it. If there is a body of mass ‘m’, then the force ${{F}_{G}}$ with which the gravity of the planet pulls towards it is given by,
${{F}_{G}}=mg$
Where ‘g’ is acceleration due to gravity.
Mass is a fundamental quantity and has the SI unit of kilogram (kg). The force has a SI unit of Newton (N). Hence from this we can conclude that,
The unit of mass is kilogram and the unit of weight is Newton.

Therefore the correct answer of the above question is option c.

Note:
Mass at a very fundamental level is a relative quantity. Mass is basically measured in grams, but gram is a unit which we assign a value with respect to the carbon atoms. Weight of a body is a consequence of mass which can easily be understood from Newton’s second law or more precisely from universal law of gravitation. It is also to be noted that weight varies from planet to planet but mass is universally constant.