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

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.

Class 10 | Gravitation

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1 / 42

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

All of the above

Gravitational force

Potential energy

Gravitational acceleration

2 / 42

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

gravitational potential.

gravitational field.

acceleration due to gravity

universal gravitational constant

3 / 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

inversely proportional to the cube

directly proportional to the square

inversely proportional to the square root

inversely proportional to the square

4 / 42

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

the feather will reach the earth first

they both will reach the earth at the same time

the stone will reach the earth first

it cannot be predicted as the given data is insufficient

5 / 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

84 N

62 N

54 N

96 N

6 / 42

The orbit of a planet is an_______with the Sun at________

hyperbolic,the centre

circular,the centre

parabolic,one of the foci

ellipse,one of the foci

7 / 42

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

lower

double

higher

zero

8 / 42

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

11.2 km/s

112 km/s

0.112 km/s

1.12 km/s

9 / 42

Law of gravitation gives the gravitational force between__________

the earth and Sun only

the earth and a point mass only

two charged bodies only

any two bodies having some mass

10 / 42

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

infinite

negative

zero

positive

11 / 42

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

It depends on the distance between two objects.

It depends on the value of the masses.

It is a force.

It does not depend on the nature of medium in which the bodies are kept

12 / 42

Medium in which true free fall is possible is ______.

moist air

water

vacuum

fluid

13 / 42

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

both (b and C)

vertically upwards

vertically downwards

away from the centre

14 / 42

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

repulsive force

Kepler's constant

gravitational force

acceleration due to gravity

15 / 42

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

The moon will collide to the earth

The moon will keep orbiting the earth

The moon will go away from the earth

The moon will travel in a straight line which is tangent to its orbit

16 / 42

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

Sun

moon

mars

planet mercury

17 / 42

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

Spacecraft getting launched from the earth's surface

Moon revolving around the earth

Stone tied to a string and rotating in a circular path

A vehicle taking a sharp turn

18 / 42

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

19 / 42

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

1/2 year

2√2 years

4 years

20 / 42

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

eight times

doubled

four times

halved

21 / 42

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

Nm/kg²

Nm²/kg

Nm/kg

Nm²/kg²

22 / 42

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

Gravitational force does not depend upon intervening medium.

Gravitational force is a weak force.

Gravitational force is always attractive

Gravitational force has a small range.

23 / 42

Uniform circular motion is possible only ______.

None

When a body is constantly acted upon by a force directed acting parallel to the surface of the circle.

When a body is constantly acted upon by a force directed towards the center of the circle

when a body is not acted by any force

24 / 42

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

Motion

Momentum

Inertia

Force

25 / 42

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

decreases

increases

increases initially and later decreases

decreases initially and later increases

26 / 42

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

will move along a straight line perpendicular to the circular path away from the boy.

will move along a straight line tangential to the circular path.

will move along a straight line towards the centre of the circular path.

will continue to move in circular path

27 / 42

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

2ve

1/2ve

4 ve

28 / 42

When an object is taken from earth to the moon,

its weight increases.

its mass decreases.

its weight remains unchanged

its mass remain unchanged

29 / 42

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

huge masses of planets, stars and other constituents of the Universe.

Large distances between the planets, stars and other constituents of the Universe.

(A) and (C)

high value of G.

30 / 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

T²r3 = constant

T²r -3 = constant

T²r = constant.

T² = constant.

31 / 42

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

U=-GMm/ RE

U=-GMm/(20 km + RE)

U=-GMm/(20,000 km + RE)

U=-GMm/( RE-20 km)

32 / 42

If the gravitational attraction of the earth suddenly disappears, then

weight of the body will become zero but the mass will remain unchanged.

both mass as well as weight will be zero

neither mass nor weight will be zero

weight of the body will remain unchanged but the mass will become zero.

33 / 42

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

Kepler's second law

Kepler's first law

Kepler's third law

Newton's law of gravitation

34 / 42

Escape velocity of a satellite depends on the

mass of the planet

mass of the satellite

radius of the orbit of the satellite

all of the above

35 / 42

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

Centripetal force

Gravitational force

Magnetic force

Centrifugal force

36 / 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.

cube

Cube root

square

square root

37 / 42

Where will it be profitable to purchase 1 kilogram sugar?

At equator

At poles

At 45°

At 40°

38 / 42

Which of the following is example of free fall?

A spacecraft with propulsion off

Descending to the earth using parachute

Flying in an aircraft

Standing an the ground

39 / 42

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

6.673 × 10 Nm/kg

6.673 x 10¹¹ Nm/ kg

6.673 × 10-¹¹ Nm2/kg2

9.673 × 10-¹¹ Nm/kg

40 / 42

The value of acceleration due to gravity

is least at the poles

is least at equator.

is maximum at the centreof the earth

is same at the equator and poles.

41 / 42

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

earth on the moon.

Sun on the earth.

moon on the earth.

earth on the sea.

42 / 42

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

Third

None

first

Second

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Chapter 1 | Gravitation | Quick Revision

Quick Revision

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