## 1. Give Reasons:

## a. Newton’s law of gravitation is known as universal law:

**Ans: **It is because Newton’s law of gravitation is true through the universe, it is true not only on the earth, but on the moon, Jupiter or in space too.

### b. A body falls faster at polar region than at equatorial region of the earth.

**Ans: **It is because, weight of object calculated by w=m eg. Mass of a body remains constant but value of ‘g’ differs from place to place and value of ‘g’ is inversely proportional to the square of radius of the earth.

### c. The force of gravitation between any two ordinary masses is not remarkable. Justify with an example.

**Ans: **It is because the gravitational force increases with the increase in mass of bodies.

### d. The value of ‘g’ varies from place to place on the surface of the earth.

**Ans:** It is because value of ‘g’ of the earth is inversely proportional to the square of its radius i.e.

### e. Weight of an object is greater of the polar region than the equatorial region of the earth.

**Ans: **It is because Weight of a body is calculated by using a formula, weight (J), mass (m) acceleration due to gravity (g), Mass of body remains constant but value of ‘g’ differs from place to place. Value of ‘g’ is inversely proportional to the square of radius of the earth. Since the polar radius of the earth is less than that of equator, the value of ‘g’ is more at the pole from at the equator.

### f. the probability of getting hurt is more when a person jumps from a large height.

**Ans: **It is because more gravitational force in the falling body in large height.

### g. The moon doesn’t have atmosphere.

**Ans:** It is because moon has less gravity.

### h. It is difficult to lift a large stone but easy to lift a smaller one on the surface of the earth.

**Ans:** It is because the large stone has higher mass than smaller one and having more mass has more gravity.

### i. It is difficult to drink water inside an artificial satellite in the space.

**Ans: **It is because artificial satellite has no gravity and inside spaceship, it feels weightlessness.

### j. A person can jump higher distance on the moon’s surface than on the earth.

**Ans: **It is because Gravity of the moon is six times less than that of the earth, so a man is attracted by the moon with six time lesser gravity than by earth.

### k. If a coin and a feather are dropped from the same height at the same time on the moon’s surface, they fall together.

**Ans:** It is because Gravity of the moon is six times less than that of the earth, therefore coin and a feather are fall together.

### l. The mass of the Jupiter is 3/9 times more than that of the earth but its gravity is only 2.5 times more than that of the earth.

**Ans:** It is because the weight of a body on a planet is the product of mass of the body and acceleration due to gravity of the planet.

### m. The parachutists are not hurt when they jump out of an aeroplane.

**Ans: **It is because in begning, it is a bundle of plastic, and shows freefall. After sometimes, it is opened and its volume is increased. It doesn’t show freefall due to air resistance.

### n. When a person jumps from aeroplane with a parachute. He can land safely on the earth surface but it is not possible on the moon.

**Ans: **It is because moon has no atmosphere. So the parachute can show freefall due to air resistance.

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## 2. Answer these questions in brief.

### a. Define the terms gravity and gravitation.

**Ans: **Gravity is the force with which the earth or any heavenly body attracts other objects towards its centre. Where as

Gravitation is the force of attraction between any two objects of the universe due to their masses.

### b. State Newton’s universal law of gravitation.

**Ans: **Newton’s universal law of gravitation states that the force of gravitation between any two bodies is directly proportional to the product of their masses and inversely proportional to the square of distance between their centres.

### c. Write down the relation of gravitational force with masses of bodies and their distance.

**Ans: **The relation of gravitational force with masses of bodies and their distance is

### d. What is gravitational constant? Write down its value.

**Ans: **Gravitational constant is the force of gravitation between two bodies each of unit mass separated by unit distance.

Its Value is 6.67×10–¹¹ Nm²/kg².

### e. Acceleration due to gravity on the moon is 1.67 m/s² what does it mean?

**Ans: **Acceleration due to gravity on the moon is 1.67 m/s² it means that mass of moon is 7.2×10²²kg and its radius is 1.7×10∧6m.

### f. Name two factors that affect gravitational force.

**Ans: **Two factors that affect gravitational force are:-

- It can observed more on liquid than on solid.
- Attraction of a big body on a small body can observed but effect of attraction of a small body on big body can’t observe.

### g. What is the value of acceleration due to gravity at the equotrial region of the earth?

**Ans: **The value of acceleration due to gravity at the equotrial region of the earth are:- 9.78 m/s².

### h. How does ‘g’ vary from place to place?

**Ans: **‘g’ vary from place to place because its value of g at the pole of earth is more but it is less at the equator.

### i. What are the factors that affect gravity?

**Ans: **– Water flows in the river.

– It causes acceleration to a falling object etc.

### j. Is there any place in the earth where the value of ‘g’ is zero?

**Ans: **The centre of the earth where the value of ‘g’ is zero.

### k. What will be the change is gravitational force if the distance between the bodies is halved?

**Ans: **Mass remains same but the distance changes when gravitational force if the distance between the bodies is halved.

### l. Under what condition, a coin and a feather fall together what is the acceleration of the feather and the coin at that instant?

**Ans: **If there is no any air to resist the falling of a body, coin and a feather fall together,

The acceleration of the feather is 0 m/s and coin acceleration is 0 m/s at the instant.

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