# KPK 9th Class Physics Chapter 5 Gravitation Short Questions Answers

KPK 9th Class Physics Chapter 5 Gravitation Short Questions with answers are combined for all 9th class(Matric/ssc) Level students.Here You can prepare all Physics Chapter 5 Gravitation short question in unique way and also attempt quiz related to this chapter.Just Click on Short Question and below Answer automatically shown. After each question you can give like/dislike to tell other students how its useful for each.

Class/Subject: 9th Class Physics

Chapter Name: Gravitation

Board: All KPK  Boards

• Malakand Board 9th Class Physics Chapter 5 Gravitation  short questions Answer
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• Swat Board 9th Class Physics Chapter 5 Gravitation short questions Answer
• Dera Ismail Khan Board 9th Class Physics Chapter 5 Gravitation short questions Answer
• Kohat Board 9th Class Physics Chapter 5 Gravitation short questions Answer
• Abbottabad  Board 9th Class Physics Chapter 5 Gravitation short questions Answer
• Bannu Board 9th Class Physics Chapter 5 Gravitation short questions Answer

• All KPK Boards 9th Class  Physics Annual Examination
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## KPK 9th Class Physics Chapter 5 Gravitation Short Questions Answers

If there is an attractive force between all objects, why do not we feel ourselves graviting toward nearby massive buildings?

Gravitational force between the different objects around us does not feel because this gravitational force is very small with respect to the earth’s mass.
Gravitational effect can be easily observed when the masses of the objects are very large i.e moon revolve around the earth due to gravitational pull.
In the other words we can say that the “G” due to very small value of G (6.67 x 10-11Nm2kg-2) gravitational force of attraction between objects around us (Building) is very small and we do not feet any attraction.

Does the sun exert a large force on the earth than that exerted on the sun by the earth? Explain.

No, the sun and earth exert same force of attraction on each other.
According to Newton’s law of Gravitation
“In the universe every object attracts very other object with same force, this force is called fore of gravitation.
This force is directly proportional to the product of their mass and inversely proportional to the square of the distance between their centers
F = GMEMs/r2
Both earth and sun exert the equal magnitude of force but the direction of these force are opposite.

What is the importance of gravitational constant “G” why is it difficult to calculate?

Importance of Gravitational Constant:
1. Revolution of moon around the earth is due to the gravitational force.
2. Gravitational force binds us to earth.
3. Earth and other planets revolve around the sun due to the gravitational force.
4. Sea waves are formed because of gravitational force between earth and moon.
The value of “G” is difficult to measure because its value is very small as compared to the other fundamental forces. Also its value is constant throughout the universe.

If earth some how expanded to a larger radius, with no change in mass, how would your weight be affected? How would it be affected if earth instead shrunk?

The value of ‘g’ is found by the formula.
g= GMe/Re2
OR            g ∝1/Re2
When ‘G’ and ‘Me are constant. The value of ‘g’ is inversely proportional to the square of Radius of earth (Re2) by increasing radius of earth the value of ‘g’ decreases, when value of ‘g’ decreases then weight of object also decreases (w=mg). so if earth expands to a larger radius, the value of ‘g’ decreases and so for weight is also decreases.
If the earth shrunk the radius decreases and so the value of ‘g’ increases and weight will also increase.

What would happen to your weight on earth if the mass of the earth doubled, but its radius stayed the same?

We know that at the surface of earth or weight is equal to the force of gravitation. i.e
F = w = GMem/Re2  ……………… (1)
If the mass of the earth is doubled then;
Me1=2Me
Now equation (1) because:
W = GMem/Re2
W’ = G(2Me)m/Re2
Me1=2Me
W’= 2 GMeM/Re2
W’= 2W
When the mass of earth because doubled then weight will also be doubled.

Why lighter and heavier objects fall at the same rate toward the earth?

Earth attracts every object either heavier or lighter. With same gravitational acceleration g = 9.8m/sec2 because the gravitational acceleration ‘g’ does not depends upon the mass of the body.
According to Galileo in the absence of resistance of air the object having same size but of different mass fall on the earth with same velocity and travel the same distance in the same time.

The value of “g” changes with location on earth, however we take same value of “g” as 9.8m/sec2 for ordinary calculation why?
The value of ‘g’ depends upon the distance from the centre of earth greater the distance from the center of earth, smaller will be the value of “g”.
Earth is not a perfectly spherical in shape that is why the value of “g” at the poles is greater then at equator.
g=GMe/Re2
On the surface of earth we take all the values of G, Me and ‘Re’ are constants. Therefore for ordinary calculation we take the value of g equal to 9.8m/sec2

Moon is attracted by the earth, why it does not fall on earth?

Moon does not fall on earth because earth is gravitational pull (Gravitational force between earth and moon) supplies necessary centripetal force to moon. Thus
Fe=FG
mmv2/R  = GMeMe/R2

Why for same height larger and smaller satellites must have same orbital speeds?

The speed of satellite is found by the formula:
V= √GMe/Re+h
Orbital speed of satellite depends upon the mass of earth and distance from the center of earth, and does not depends upon the mass of satellite.
Therefore the same height larger and smaller satellites have same orbital speed.

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