Page No 138: - Chapter 10 - Gravitation - Ncert Solutions class 9 - Science
Updated On 26-08-2025 By Lithanya
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Question 1:
What are the differences between the mass of an object and its weight?
Answer:
|
S. No. |
Mass |
Weight |
|
I. |
Mass is the quantity of matter contained in the body. |
Weight is the force of gravity acting on the body. |
|
II. |
It is the measure of inertia of the body. |
It is the measure of gravity. |
|
III. |
Mass is a constant quantity. |
Weight is not a constant quantity. It is different at different places. |
|
IV. |
It only has magnitude. |
It has magnitude as well as direction. |
|
V. |
Its SI unit is kilogram (kg). |
Its SI unit is the same as the SI unit of force, i.e., Newton (N). |
Question 2:
Why is the weight of an object on the moon 
th its weight on the earth?
Answer:
Let ME be the mass of the Earth and m be an object on the surface of the Earth. Let RE be the radius of the Earth. According to the universal law of gravitation, weight WE of the object on the surface of the Earth is given by,
Let 
and 
be the mass and radius of the moon. Then, according to the universal law of gravitation, weight WM of the object on the surface of the moon is given by:
Therefore, weight of an object on the moon is of its weight on the Earth.
