Page No 143: - Chapter 10 Gravitation class 9 ncert solutions Science - SaraNextGen [2024-2025]

Updated By SaraNextGen

On April 24, 2024, 11:35 AM

Question 1:

How does the force of gravitation between two objects change when the distance between them is reduced to half?

Answer:

According to the universal law of gravitation, gravitational force (F) acting between two objects is inversely proportional to the square of the distance (r) between them, i.e.,

If distance r becomes r/2, then the gravitational force will be proportional to 

Hence, if the distance is reduced to half, then the gravitational force becomes four times larger than the previous value.

Question 2:

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, called acceleration due to gravity (in the absence of air resistances). It is constant and does not depend upon the mass of an object. Hence, heavy objects do not fall faster than light objects.

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:

According to the universal law of gravitation, gravitational force exerted on an object of mass m is given by:

Where,

Mass of Earth, M = 6 × 10²⁴ kg

Mass of object, m = 1 kg

Universal gravitational constant, G = 6.7 × 10⁻¹¹ Nm² kg⁻²

Since the object is on the surface of the Earth, r = radius of the Earth (R)

r = R = 6.4 × 10⁶ m

Gravitational force, 

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:

According to the universal law of gravitation, two objects attract each other with equal force, but in opposite directions. The Earth attracts the moon with an equal force with which the moon attracts the earth.

Question 5:

If the moon attracts the earth, why does the earth not move towards the moon?

Answer:

The Earth and the moon experience equal gravitational forces from each other. However, the mass of the Earth is much larger than the mass of the moon. Hence, it accelerates at a rate lesser than the acceleration rate of the moon towards the Earth. For this reason, the Earth does not move towards the moon.