1. Gravitational force acts on all objects is proportional to their masses. Why, then a heavy object does not fall faster than a light object?
2. Why will a sheet of paper fall slower than one that is crumbled into a ball ?
3. What happens to the force between two objects , if the mass of one object is doubled?
4. What is the acceleration of free fall?
5. A body is thrown vertically upwards and rises to a height of 10m. Calculate (i) the velocity with which the body was thrown upwards and (ii) the time taken by the body to reach the highest point?
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Answers
Question1.
How does the force of gravitation between two objects change when the distance between them is reduced to half?
Answer:
According to Universal law of gravitation, the force of attraction between 2 bodies is:-
F = (G m1m2)/r2
Where m1m2 = the masses of the two bodies,
r = distance between them
G = gravitational Constant
When the distance is reduced to half i.e. r’ = (1/2) r then,
F’ = (G m1m2)/r2
= (G m1m2)/(r/2)2
= (4 G m1m2)/ (r2) = 4F
Therefore when the distance between the objects is reduced to half, then the force of gravitation increases by four times the original force.
Question2.
Gravitational force acts on all objects in proportion to their masses. Why then, a heavy object does not fall faster than a light object?
Answer:
All objects fall on ground with constant acceleration known as acceleration due to gravity (g).
It is constant and the value of ‘g’ does not depend upon the mass of an object.
Therefore heavy objects do not fall faster than light objects provided there is no air resistance.
Question 3.
What is the magnitude of the gravitational force between the earth and a 1 kg object on its surface?
(Mass of the earth is 6 × 1024 kg and radius of the earth is 6.4 × 106 m.)
Answer:
Given:
Mass of earth m1 =6 × 1024 kg
Mass of the object m2 = 1 kg
Radius of the earth =6.4 × 106 m
Universal gravitational constant G = 6.67 x 10-11 Nm2kg-2
By applying universal law of gravitation: - F = (G m1 m2/r2)
= (6.67 x 10-11 x 6 × 1024 x 1)/ (6.4 × 106)2
F = 9.8 N
Physics Class 9 Gravitation Image 4
Question 4.
The earth and the moon are attracted to each other by gravitational force.
Does the earth attract the moon with a force that is greater or smaller or the same as the force with which the moon attracts the earth? Why?
Answer:
The earth attracts the moon with an equal force with which the moon attracts the earth but these forces are in opposite directions.
By universal law of gravitation, the force between moon and the sun will be:
F = (G m1 m2/d2)
Where m1 m2 = masses of earth and moon respectively.
d = distance between the earth and moon.
Question 5.
If the moon attracts the earth, why does the earth not move towards the moon?
Answer:
According to universal law of gravitation and Newton third law, we know that the force of attraction between two objects is same but in opposite direction.
Thus the earth attracts the moon with the same force as the moon exerts on earth but in opposite directions.
This ans is from exam fear site
Answer:
a.Gravitational force acts on all objects in proportion to their masses. But a heavy object does not fall faster than a light object. This is because of the reason that Acceleration= Force/Mass or Force = Acceleration x Mass As force is directly proportional to mass, acceleration is constant for a body of any mass.
b.As air applies some resistance on falling sheet of paper as well as crumpled ball but the resistance to the motion of crumpled ball through the air decreases that makes it to fall faster than the sheet of paper.
c. If the mass of both of the objects is doubled, then the force of gravity between them is quadrupled; and so on. Since gravitational force is inversely proportional to the square of the separation distance between the two interacting objects, more separation distance will result in weaker gravitational forces.
d.An object that is moving only because of the action of gravity is said to be free falling and its motion is described by Newton's second law of motion. ... The acceleration is constant and equal to the gravitational acceleration g which is 9.8 meters per square second at sea level on the Earth.
e. is explained in the pic above
