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If we take = 1. Then the inertial mass and gravitational mass are equal.
2
For example, it is difficult to accelerate or decelerate a heavy football player compared to a light

player. This is because his inertial mass is greater. It is harder to carry off the heavy player out of the

court when he is hurt. This is due to greater gravitational mass.

Mass and density of Earth:

Using the law of universal gravitation and the measured value of g, we can
find the mass and density of earth.

(i) Mass of Earth (M):

The acceleration due to gravity on the surface of earth is given by:

g =
2 2

Or, M = ……….(i)

We know, g = 9.8m/ 2

Radius of earth (R) = 6.37 x 10 m
6
2
Gravitational Constant (G) = 6.67 x 10 −11 N −2
Thus, equation (i) gives,

Mass of earth (M) = 6 x 10 24 kg (approx.)