KENDRITYA VIDYALAYA
SANGATHAN
KVS RO KOLKATA
SESSION 2023-24
STUDY MATERIAL FOR SLOW
ACHIEVERS
CLASS- XI PHYSICS
CHAPTER: 8 GRAVITATION
Q CORE QUESTION MARK
NO. CONCEPT/
FOCUSED-
FORMULA/
TARGATED
THEOREM
SECTION -A: MCQ (QN NO 1-15)
1 Newton’s law Two identical spheres of radius R made of the same material are kept at 1
of Gravitation a distance d apart. Then the gravitational attraction between them is
proportional to
(a) d–2 (b) d2 (c) d4 (d) d
2 Escape The Escape velocity from the Earth for a body of 20 g is 11.2 km/s. 1
velocity does What will be its value for a body of 100 g?
not depend on
mass of the
object (a) 1.12 km/s (b) 112 km/s (c) 11.2 km/s (d) 0.112
km/s
3 Newton’s law Which one of the following statements is true for the relation 1
of Gravitation F= Gm1 m2/ r2 ? (All symbols have their usual meanings)
(a) The quantity G depends on the local value of g, acceleration due to
gravity
(b) The quantity G is greatest at the surface of the Earth
(c) The quantity G is used only when earth is one of the two masses
(d) The quantity G is a universal constant
4 Gravitational Which one of the following statements about gravitational force is NOT 1
force correct?
(a) It is experienced by all bodies in the universe
(b) It is a dominant force between celestial bodies
(c) It is a negligible force for atoms
(d) It is same for all pairs of bodies in our universe
5 Atmosphere There is no atmosphere on the moon because 1
on moon (a) it is closer to the earth
(b) it revolves round the earth
(c) it gets light from the sun
(d) the escape velocity of gas molecules is less than their root mean
square velocity here.
6 Variation og g At what distance from the centre of the earth the value of acceleration 1
with height due to gravity g will be half that on the surface (R=radius of earth)?
(a) 2R (b) R (c) 1.414R (d) 0.414R
7 Variation of g The value of acceleration due to gravity, at earth surface is g. Its value 1
with depth at the centre of the earth, which we assume as a sphere of radius R and
of uniform mass density, will be:
(a) 10 R m/s2 (b) zero (c) 5 R m/s (d) 20 R m/s2
8 Acceleration Find ratio of acceleration due to gravity g at depth d and at height h, 1
of Gravity where d = 2h.
(a) 1 : 1 (b) 1 : 2 (c) 2 : 1 (d) 1 :
4
9 Variation of g The radius of earth is about 6400 km and that of mars is about 3200 km. 1
in other planet The mass of the earth is about 10 times of the mass. The object weighs
200 N on earth surface, then its weight on the surface of mars will be
(a) 80 N (b) 40 N (c) 20 N (d) 8 N
10 Elliptical Earth is flattened at poles and bulging at the equator. This is due to 1
shape of Earth
(a) centrifugal force is less at the equator than at poles
(b) angular velocity is more at poles
(c) centrifugal force is more at the equator than at poles
(d) None of the above
11 Variation of g When a body is taken from poles to equator on the earth, its weight 1
from poles to
equator (a) increase
(b) decrease
(c) remains the same
(d) increase at south pole and decreases at north pole
12 Motion under A piece of paper and a coin both having the same mass are dropped 1
gravity from the 10th floor of a building. The piece of paper would take more
time to reach the ground because
(a) gravitational pull on the paper is less than the coin
(b) buoyant force on the piece of paper is more than that on the coin
(c) buoyant force on the coin is more and acts in the downward
direction
(d) the piece of paper takes a longer path to reach the ground
13 Relation IF vo and ve represent the orbital velocity and escape velocity of a 1
between satellite corresponding to a circular orbit of radius R, then.
escape
velocity and (a) ve and vo are not related (b) vo= ve/√2
orbital (c) ve = vo (d) ve = vo/√2
velocity
14 Acceleration Two spheres of same size one of mass 2 kg and another of mass 4 kg are 1
due to gravity dropped simultaneously from the top of Qutab Minar (height = 72m).
When they are 1 m above the ground, the two spheres have the same:
(a) momentum
(b) kinetic energy
(c) potential energy
(d) acceleration
15 Keplar’s Keplar’s second law depends on 1
second law of
planetary (a) Conservation of angular momentum
motion (b) Conservation of area
(c) Conservation of energy
(d) Non of these
SECTION -B: ASSERTION REASONING QUESTIONS: (QN 1
NO 16-20)
Assertion: (A). 1
Reason: (R)
CHOOSE THE CORRECT OPTION AS PER THE STATEMENTS
GIVEN IN ASSERTION AND REASON:
a) Assertion and Reason both are correct and R is the correct
explanation of A.
b) Assertion and Reason both are correct but R is not the correct
explanation of A.
c) Assertion is true but Reason is false.
d) Assertion and Reason both are incorrect.
16 Keplar’s third Assertion (A) : The time period of revolution of a satellite close to 1
law of surface of earth is smaller than that revolving away from the surface of
planetary earth.
Motion Reason (R) : The square of time period of revolution of a satellite is
directly proportional to cube of its orbital radius.
17 Gravitational Assertion (A) : An artificial satellite moving in a circular orbit around 1
potential the earth has a total energy (i.e. sum of potential & kinetic energy) E. Its
energy potential energy -E.
Reason(R) : Potential energy of the body at a point in a gravitational
field of earth is -GMm/ 2R .
18 ESCAPE Assertion (A) :Escape speed for the moon is 2.3km/s which is 5 times 1
VELOCITY smaller than that of earth.
Reason (R) : The escape speed depends upon acceleration due to
gravity on the moon and radius of the moon and both of them are
smaller than the earth.
19 Gravitation in Assertion : Moon travellers tie heavy weight at their back before 1
moon landing on the moon.
Reason : The acceleration due to gravity on moon is smaller than that
of earth.
20 Acceleration Assertion: The acceleration due to gravity increases with height above 1
due to gravity the earth's surface.
Reason: Gravitational force increases with height.
SECTION -C: CREATIVE AND CRITICAL THINKING
QUESTIONS: (QN NO 21-22)
21 Keplar’s laws The Distance of two planets from the sun are A 1011 m and 1010 m 1
respectively .What is the ratio of time period of these two planets?
22 Gravitational An astronaut orbiting the earth in a circular orbit 120Km above the 1
field in outer surface of Earth gently drops a pen out of space-ship. What can you say
space about the motion of the pen.
SECTION -D: VERY SHORT ANSWER QUESTIONS: (QN NO
23-29)
FREQUENTLY ASKED QUESTIONS: [Qn 23-26]
23 Variation of g Draw and exaplain the graphs showing the variation of acceleration due 2
with height
to gravity with
and depth
(a)height above the earth’s surface,
(b)depth below the Earth’s surface.
24 Varition of g If a person goes to a height equal to radius of the earth from its surface. 2
with height
What would be his weight relative to that on the earth.
25 Acceleration Why does moon have no atmosphere? 2
due to gravity
on moon
26 Variation of g The mass and diameter of a planet have twice the value of the 2
in other corresponding parameters of the earth. What is the acceleration due to
planets gravity on the surface of the planet?
MOST IMPORTANT QUESTIONS (AS PER CONCEPT/ LEARNING
OUTCOME OF THE CHAPTER) [Qn 27-29]
27 Gravitational A body weighs 63 N on the surface of the earth. What is the 2
force gravitational force on it due to the earth at a height equal to half the
radius of the earth?
28 Escape Two planets A and B have their radii in a ratio ‘r’. The ratio of the 2
velocity acceleration due to gravity on the planets is’ x’. What is the ratio of the
escape velocity from the two planets?
29 Gravitational A satellite orbits the earth at a height of 500 km from its surface. 2
energy Calculate the kinetic energy, potential energy and total energy of the
satellite.
Given: Mass of the satellite = 300kg
Mass of the earth = 6 x 10 24 kg
Radius of the earth = 6.4 X 10 6m
G = 6.67 x 10 -11 Nm2 kg-2
SECTION -E: SHORT ANSWER QUESTIONS: (QN NO 30-36)
FREQUENTLY ASKED QUESTIONS: (Qn 30-33)
30 Keplar’s laws Write Keplars three laws of planetary motion 3
31 Gravitational Show that the gravitational potential at a point of distance R from the 3
potential mass M is given by V = - (GM/R). what does the negative sign indicate
32 Escape Derive an expression for finding the escape velocity of a body from the 3
velocity surface of the earth.
33 Weight at the Show that weight of all objects will be zero at the Centre of earth? 3
centre of earth
MOST IMPORTANT QUESTIONS (AS PER CONCEPT/ LEARNING
OUTCOME OF THE CHAPTER) (Qn 34-36)
34 gravitational A mass 'M' is broken into two parts of masses m1 and m2. How are m2 3
attraction and M related so that force of gravitational attraction between the two
parts is maximum.
35 Escape The escape velocity of a projectile on the earth surface is 11.2 Km/s. A 3
velocity of a body is projected out with thrice this speed. What is the speed of the
projectile on body far away from the earth? Ignore the presence of the Sun and other
the earth planets
.
36 Escape speed Explain how does the escape speed of a body from the earth depend on 3
(i) mass of the body
(ii) the location from where it is projected
(iii) the height of the location from where the body is launched?
SECTION -F: CASE STUDY BASED QUESTIONS: (QN NO 37-
38)
37 Gravitation 4
Gravitation What do aching feet, a falling apple, and the orbit of the Moon have in
common? Each is caused by the gravitational force. Our feet are
strained by supporting our weight—the force of Earth’s gravity on us.
An apple falls from a tree because of the same force acting a few meters
above Earth’s surface. And the Moon orbits Earth because gravity is
able to supply the necessary centripetal force at a distance of hundreds
of millions of meters. In fact, the same force causes planets to orbit the
Sun, stars to orbit the center of the galaxy, and galaxies to cluster
together. Gravity is another example of underlying simplicity in nature.
It is the weakest of the four basic forces found in nature, and in some
ways the least understood. It is a force that acts at a distance, without
physical contact, and is expressed by a formula that is valid everywhere
in the universe, for masses and distances that vary from the tiny to the
immense.
Sir Isaac Newton was the first scientist to precisely define the
gravitational force, and to show that it could explain both falling bodies
and astronomical motions. See Figure . But Newton was not the first to
suspect that the same force caused both our weight and the motion of
planets. His forerunner Galileo Galilei had contended that falling bodies
and planetary motions had the same cause. Some of Newton’s
contemporaries, such as Robert Hooke, Christopher Wren, and Edmund
Halley, had also made some progress toward understanding gravitation.
But Newton was the first to propose an exact mathematical form and to
use that form to show that the motion of heavenly bodies should be
conic sections—circles, ellipses, parabolas, and hyperbolas.
Q:1Two astronauts are floating in gravitational free space after having
lost contact with their spaceship. The two will
a) move towards each other
b) move away from each other
c)will become stationary
d) keep floating at the same distance between them
Q:2 Two spheres of masses m and M are situated in air and the
gravitational force between them is F. The space around the masses is
now filled with a liquid of specific gravity 3. The gravitational force
will now be
a) 3F
b) F
c) F/3
d) F/9
Q:3 A ball of weight W is thrown vertically upwards. The apparent
weight during the upward motion will be
(a) zero
(b) more than W
(c) less than W
(d) W
Q:4 If the distance between the earth and the sun were half its present
value, the number of day in a year would have been
(a) 64.5
(b) 129
(c) 182.5
(d) 730
38 Geostationary Geostationary satellite 4
satellite
Geostationary satellite is the best spot for communications satellites to
use, however. This is a zone above Earth's equator at an altitude of
35,786 km.
At this altitude, the rate of "fall" around the Earth is about the same as
Earth's rotation, which allows the satellite to stay above the same spot
on Earth almost constantly. The satellite thus keeps a perpetual
connection with a fixed antenna on the ground, allowing for reliable
communications. When geostationary satellites reach the end of their
life, protocol dictates they're moved out of the way for a new satellite to
take their place. That's because there is only so much room, or so many
"slots" in that orbit, to allow the satellites to operate without
interference. While some satellites are best used around the equator,
others are better suited to more polar orbits — those that circle the Earth
from pole to pole so that their coverage zones include the north and
south poles. Examples of polar-orbiting satellites include weather
satellites and reconnaissance satellites.
Q:1 Most waves used for communication purposes rely on
geostationary satellites because _____
a) they cannot transmit data at long distances due to curvature of the
earth
b) they are reflected by the atmosphere
c) they are very cheap
d) it does not occupy space on the earth’s surface
Q:2 A geostationary satellite seems to be fixed in the sky because it
does not orbit the earth.
a) True
b) False
Q:3 The height of the geostationary satellites above the earth’s surface
is approximately
a) 36,000 km
b) 72,000 km
c) 15,000 km
d) 30,000 km
Q:4 Polar satellites are used for high-resolution imaging of the earth’s
surface because
a) they have better cameras
b) they are very high above the surface of the earth and travel slowly to
gather more information
c) they are closer to the surface of the earth and can cover vast areas
very quickly
d) they can be launched by most countries in the world
SECTION -G: LONG ANSWER QUESTIONS: (QN NO 39-40)
39 Newton’s I. State Newton’s universal law of gravitation. 5
universal law II. Find the relation between universal gravitational constant and
of gravitation acceleration due to gravity.
III. The mass and diameter of a planet are twice those of the earth.
What will be the period of oscillation of a pendulum on this
planet, If it is a second’s pendulum on the earth?
40 Variation of g I. Deduce the formula for the variation of g with height ‘h’ above 5
with height the surface of the earth
II. How far away from the surface of earth does the value of g is
reduced to 4% of its value on the surface of the earth
Given radius of earth = 6400km
ANSWER KEY:
Q.NO. Answer MARK
SECTION -A: MCQ (QN NO 1-15) [Answer explanation]
1 (a) : According to Newton's law of gravitation F = GMm/ d2 hence Fα d-2 1
2 (c) : Escape velocity ve= √2gR does not depend on the mass of the object. 1
3 (d) : Gravitational Force F = GMm/ R2 1
Where, m1 = mass of first body m2 = mass of second body r = distance between two
body
G = Gravitational constant G is the universal gravitational constant which remain
constant at all places in the universe G is equivalent to the force of all reaction between
two bodies of unit mass and unit distance apart. The value of G = 6.67 × 10–11 Nm2
/kg2
4 (d) : Gravitational force isn't same for all pairs of bodies in our universe. It will vary 1
with different masses and distance between them because it depends on their masses
and distance between them.
5 (d) the escape velocity of gas molecules is less than their root mean square velocity 1
here.
