Mass


Gravitation - Concepts
Class - RRB Technician Grade I Signal Subjects
 
 
Concept Explanation
 

Mass

Mass: The mass is the total content of the body which measures the inertia of a body. It is a scalar quantity and its SI unit is kilogram. Irrespective of the position of the body in the universe, mass always remains constant everywhere. The mass of the body cannot be zero.

Inertial mass and Gravitational mass:

Inertial mass: Inertial mass of a of a body is related to its inertia of linear motion, and is defined by newton's second law of motion.

Let a body of mass m moves with acceleration a underaction of an external force F. According to the Newton's second law of motion

                                     F ;=:ma::: or:;; m ;=:;frac{F}{a}

The mass of the body in this sense is called as the inertial mass of the body. If a = 1, then from above equation m = F

Thus inertial mass of a body is equal to the magnitude of external force required to produce unit acceleration in the body.

Gravitational mass: 

Gravitational mass of a body is related to gravitational pull of the body and is defined by Newton's law of gravitation.If a body of mass m_G is placed on the surface of the earth of radius R and mass M,then gravitational pull on the body is given by 

F:=:frac{GMm_G}{R^2}:Rightarrow m_G:=:frac{F}{frac{(GM)}{(R^2)}};=;frac{F}{J}

The mass  m_G  of the body in this sense is the gravitational mass of the body. The inertia oft he body has no effect on the gravitational mass of the body.If J = 1 then from the equation m_G = F.

Thus gravitational mass of the body is defined as the magnitude of gravitational pull experienced by the body in gravitational field of unit intensity.

Sample Questions
(More Questions for each concept available in Login)
Question : 1

What is the SI unit of mass ?

Right Option : B
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Question : 2

A person of mass 'm' is standing on a platform. if the platform freely moving downwards, normal reaction acting on the person is

Right Option : C
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Question : 3

Which of the following are correct :

(a) The mass of the body can be zero.

(b) The mass of the body cannot be zero.

Right Option : B
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