Chapter 1 | Gravitation | Quick Revision

Quick Revision

1. Force and Motion:

A force acts on any object moving along a circle and it is directed towards the centre of the circle. This is called the centripetal force.

2. Kepler’s Laws:

(i) Kepler’s first law: The orbit of a planet is an ellipse with the sun at one of the foci.

(ii) Kepler’s second law: The line joining the planet and the Sun sweeps equal areas In equal Intervals of time.

(iii) Kepler’s third law: The square of its period of revolution around the Sun is directly proportional to the cube of the mean distance of a planet from the Sun. 

T2∝a3, where T is the time period and a is the orbital radius.

3. Newton’s Universal Law of Gravitation:

(i) Newton’s Universal Law of Gravitation: Everybody in this universe attracts every other body with a force, which is directly proportional to the product of their masses and inversely proportional to the square of the distance between their centres.

(ii) According to Newton, the gravitational force acting between two bodies, 

F∝m1m2d2 or  F=Gm1m2d2

where G is the universal gravitational constant.

4. Earth’s Gravitational Acceleration:

(i) Acceleration due to gravity is the acceleration with which a body falls freely towards any heavenly body such as Earth. Its mean value on Earth is 9.81 m/s2.

(ii) Acceleration due to gravity is maximum at poles. Its value decreases towards the equator, high up in the mountains, deep inside the earth and in space. Its value is zero at the centre of the Earth.

5. Mass and Weight:

(i) Mass is the amount of matter contained in a body. It is a scalar quantity, and its SI unit is kilogram (kg).

(ii) Weight is the pull exerted on a body by the Earth. It is a vector quantity, and its SI unit is Newton.

6. Free Fall:

(i) Equations of motion for a freely falling body are:

(a) v=u+gt

(b) h=ut+12gt2

(c) v2−u2=2gh

Where u is the initial velocity, v is the final velocity; g is the acceleration due to gravity; h is the height and t is the time in seconds.

7. Gravitational Potential Energy:

When an object is at a height h from the surface of the earth, its potential energy is,

PE=−GMmR+h, where M and R are the earth’s mass and radius respectively.

8. Escape Velocity:

(i) The velocity required for an object to overcome the gravitational pull of the earth and escape to space is called the escape velocity.

(ii) The equation for escape velocity is, v=gR−−−√, where g is the acceleration due to gravity of the planet and R is the radius of the planet.

(iii) For Earth, the value of escape velocity is 11.2 km/s.

gravitation

Class 10 | Gravitation

1 / 42

The tidal waves in the sea are primarily due to gravitational effect of

2 / 42

The orbit of a planet is an_______with the Sun at________

3 / 42

The square of orbital period of revolution of a planet is directly proportional to the_____of the mean distance of the planet from the sun.

4 / 42

Where will it be profitable to purchase 1 kilogram sugar?

5 / 42

The earth revolves around the Sun in one year.If the distance between them becomes double,the new period of revolution will be

6 / 42

Escape velocity of a satellite depends on the

7 / 42

If the gravitational attraction of the earth suddenly disappears, then

8 / 42

In SI units, the value of G is equal to the _______ between two masses of 1 kg kept 1 m apart.

9 / 42

Which of the following in NOT a characteristic of gravitational force?

10 / 42

Force which is directed towards the center of the circle is ______.

11 / 42

The direction of the acceleration due to gravity of any object is always_______.

12 / 42

A boy is whirling a stone tied to a string in a horizontal circular path. If the string breaks, the stone

13 / 42

In which of the following cases centripetal force is not experienced?

14 / 42

The minimum velocity of the spacecraft to escape from earth’s gravitational force must be ______.

15 / 42

Value of acceleration due to gravity (g)_________as we go deep insider the earth.

16 / 42

Accordinfg to Kepler,the period of revolution of a planet(T) and its mean distance grom the sun(r) are related by the equation

17 / 42

on the value of acceleration due to gravity is ⅙ times that on the surface of the earth.

18 / 42

According to Newton’s first law of motion, higher the mass _______is the inertia.

19 / 42

Uniform circular motion is possible only ______.

20 / 42

The value of acceleration due to gravity

21 / 42

The force of attraction between two-unit point masses separated by a unit distance equals

22 / 42

Which is the gravitational potential energy of an object located 20,000m above the earth’s surface ?

23 / 42

What would happen to the moon if the earth stops exerting force of attraction on it?

24 / 42

Escape velocity on a planet is ve. If radius of the planet remains same and mass becomes 4 times, the escape velocity becomes

25 / 42

Which of the following is example of free fall?

26 / 42

According to Newton’s _______ law of motion, a force acting on a body results in its acceleration.

27 / 42

When an object is taken from earth to the moon,

28 / 42

Though the gravitational force is much weaker than other forces in nature but it controls the Universe because of the ______.

29 / 42

When distance between two objects is decreased by d times, the gravitational force between them increases 4 times. The value of d is ________.

30 / 42

The gravitational force between two bodies is directly proportional to the product of the masses of those bodies and is_________of the distance between them

31 / 42

If mass of one of two objects is doubled then the gravitational force acting between the two is _______

32 / 42

Which of the following statements about the gravitational constant is true?

33 / 42

The value of universal gravitational constant (G) in SI unit is _______.

34 / 42

The value of g on moon 1/6th of its value on the earth. If a person weighs 14 N on the moon’s surface, then the weight of the person on earth’s surface is

35 / 42

A ______ is necessary to change the speed as well as the direction of motion an object.

36 / 42

Which of the following is the S.I. unit of universal gravitational constant?

37 / 42

Acceleration of an object throw upwards is always taken _______as it moves against the force of gravity.

38 / 42

Which of the following law states areal velocity of the planet remains constant?

39 / 42

If earth’s satellite is moved from one stable orbit to a father stable orbit, then which of the following quantities increase?

40 / 42

When a feather and a heavy stone are dropped from a same height at the same time in vacuum

41 / 42

Medium in which true free fall is possible is ______.

42 / 42

Law of gravitation gives the gravitational force between__________

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