)~ , / ' OBJECTIVE TYPE QUESTIONS

bit flattened. So the acceleration due to gravity

experienced at the poles is slightly higher than
that at the equator.
Q. 3. The gravitational force between two objects is R
Q.1. Two objects of different masses falling freely
If masses of both objects are halved without
near the surface of Moon would : ·
changing distance between them, then the
• • (A) Have same velocities at any instant
• ,
1
•
gravitational force would become
(B) Have different accelerations . \,
• I •
(C) Experience forces of same magnitude · (A) F (B) F
- (D) Undergo a change in their inertia. 4 2
Ans. Option (A) is correct. (QF (D)2F
Explanation: Objects of different masses falling Ans. Option (A) is correct.
freely near the surface of the.Moon would have Explanation: We know that, according to force of
the same velocities at any instant because they gravitation,
will have same acceleration due to gravity. Gm1ni
Q. 2. The value of acceleration due.to gravity: , F = 1 (G =Gravitational constant)
r
. ~ l , _ • ,. (A) is same on equator and poles

·, .~-.·. <.-. (II) is least on.poles _ . , where m1 ·and m2 are the masses of two objects
(q is least on equator · ·, respectively. And r is the distance between the ·
l· , . , \ A· (D)Increases from pole to equator two masses
Ans. Option (Q is correct. N~w, according to the question, if masses of both
Explanation: Due to structure of ~ as on the objects are halved. i.e.,
equator Earth is bulging out and at poles it is a

\
 GRAVITATION ~
m' = Int andm2'=m2 Explanation: G is called the universal
I I 2 2 gravitational constant. It is independent of mass
and radius of the Earth.
Newforce,
F';, Gm\m' 2 G(~)(~) Q.8. Two particles are placed at some distance. If the
r2 r2 mass of each of the two particles is doubled,
=.!. Gm1m2 =£.where Gm1m2 =F keeping the distance between them unchanged,
4 r2 4 r2 the value of gravitational force between them
So, new force, F' = £. will be:
4
(A)! times (B) 4times
Thus, the new gravitational force will become .!. 4
times of its original gravitational force. 4
Q. 4• A b?y is whirling a stone tied with a string in a (C) ! times (D) unchanged
honzontal circular path. If the string breaks, the 2
stone ·
Ans. Option (B) is correcL
(A) Will continue to move in the circular path. Explanation: We know that, according to
(B) Will move along a straight line towards the gravitational force
centre of the circular path.
F=GMm ...(Eq.l)
(C) Will ?'ove along a straight line tangential to ,2
(D) :ill
. the cucular path. ' . ,
m~ve al~ng a straight line perpendicular
· • . the ~c~ar path away from the boy.
Where, F = Force between two masses
M = First mass
Ans. Option (C) 1s correcL ·, m = Second mass
Expl~nation: In circular motion the directi f G = Gravitational constant
velooty at . . , on o
' . a po~t IS always along the tangent at r = Distance between two masses
. that po~t. If string breaks, then the centripetal
According to the question,
, fo~e acting on the stone becomes zero and it
.- will ~ove along F' = New force when mass is doubled
, a ,.straight line tangential t o the
circular path.·. . . H'mass of each particle is doubled
Q. 5. In the_relation F = GM m!d2, the quantity G : i.e., M = 2Mand m = 2m
(A) Depe_nds on the value of g at the place of On putting these values in Eq.(1), we get
· observation -· :
(B) Is ~ed only ,w he~ the Earth is one of the two F'=G(2M)(2m)
masses · · '
,2
(C) Is greatest at the surface of th~ Earth Because, F = GMm
(D)Is universal constant of natme. , r2
Ans. Option (D) is correct. . . . . : -.. •- -· ,.J So, F'= 4F
Explanation: The quantity G is universal constant Q. 9. The atmosphere is held to the Earth by :
of 1:ature. It is applied to all the bodies present in _ (A)Gravity ,, _ • , • • . , .
uruverse. (B) Wmd · . • ' " .' ..
0 ..~

Q. 6. Law of gravitation gives the gra;itational force (C)Oouds

between :. . . .- (D) Earth's magnetic field
(A) The Earth and a point mass only · Ans. Option (A) is correcL · . •
(B) The Earth and the sun only : Explanation: The atmosphere is held to the Earth
(C) Any two bodies having some mass by gravity. . , • . , , , · • · · . · · ,
(D)'l\vo charged bodies only Q. 10. · The force of attraction between two unit
Ans. Option (C) is correcL point masses separated by a unit distance is
Any two bodies having some mass. called: .
Explanation: Law of gravitation gives the (A) Gravitational potential
gravitational force between any two bodies (B) Acceleration due to gravity
having same mass. · · • (C) Gravitational field
Q, 7• . The value of quantity Gin the law of gravitation: (D)Universal constant
(A) Depends on mass of the Earth only · Ans·. ' Option (D) is correct. . , · , , , · ,.
(B) Depends on radius of Earth only Explanation: The force of attraction between two
(C) Depends on both mass and radius of the unit point masses separated by a unit distance is
" Earth called universal gravitational constant.
(D)Is independent of mass and radius of the Q. 11. The weight of an object at the centre ·of the Earth
Earth. . of radius R, is : · · '
Ans. Option (D) is correcL (A)Zero · '
(B) Infinite
 Oswaal CBSE Question Banlc Chapterwise & Topicwise,
SCIENCE, Class-IX
. A is false but reason
(R) .
1s true,
Ii1

(D)Assertton ( ) fan object is always zero.

(C) R times the weight at the surface of the Earth rtion•Massfoan object is the measure of its
Q. 1. Asse · O
(D) ; 2 times the weight at the surface of the Reason : Mass bstance contained by the bod"J•
. . . ' inertia and the su
• (D) is correct.
Earth. Ans, Op tion . . Mass of an object can never be zero
Ans. Option (A) is correct an
ExplattlltiDtl• f object is the measure of its
Explanation: The weight of an object at the beca ~ ~a: :ubstance contained by the body.
centre of the Earth of radius R is zero. . inertia. an . ~ Moon, man feels lighter than

I
Q. 2. Assertion •
Q.12. An apple falls from a tree because of • ati'onal force exerted f
Earth, .
to more gravit
gravitational attraction between the Earth and Reason: Due
apple. If F1 is the magnitude of force exerted by by Moon on man.
t. . . ·
the Earth on the apple and F2 is the magnitude 0 ti·on (C) is correc , man feels lighter than '·.
Ans. P . • On Moon
of force exerted by apple on Earth, then : to less gravitationa l force exerted
(A) F1is very much greater than F2 Earth. ttll~d·
Expla It 1s ue ,
t
(B) F2 is very much greater than F1 by Moon on man.
.on • If the distance b~ee n two bodies I
(C) F1 is only a little greater than F2 Q, 3. Asserti · and m2 is increased by· a factor of 5 ff
of mass m1 1 '
(D)F1 and F2 are equal
Ans. Option (D) is correct · 'tati' nal force is reduc ed by - .
the gravt O . . • 2?
Explanation: According to Newton's universal . The o-ravitational force 1s inversely
law of gravitation, force exerted by the one body Reaso n. rr.· the square Of the disi~-
. al . to u1..11ce
,.
.propo rti on
to other body is equal in magnitude and opposite between two bodies. ·
in direction. · · ·· ·
. Ans. Option (A) is correc t. . . .
Explanation: Gravitational force IS given by
GMm G . ti' alf
the formula F = : Ji2 .. ravita on orce
-~ '- in~~rsely pr~portional to the square of the
distance between two bodies.
Q:4.· ·Assertion ·=An obj~ thrown verti~ally up":ard
·, with certain velocity v, reaches maximum height
Directions: In the following questions, a statement and fall back with same velocity.
of assertion (A) is followed by a statement of . ' ·· . Reason : Whenever an object falls towards the
reason (R). Mark the correct choice as: ., Earth, gravitational force of the Earth causes
(A) Both assertion (A) and reason (R) are true ' accele ration.
• . and reason (R) is the correct explanation of Ans. Option (D) is correct
· . assertion (A). ' ·, · Explanation: When an object is thrown vertically
(B) Both assertion ·(A) and reason (R) are 'true , upward with certain velocity, it will fall back
. but reason (R) is not the correct explanation '
1 freely. There will be a change in the magnitude
of assertion (A). of velocity due gravitational force of the Earth.
(Q Assertion (A) is true but reason (R) is_false.

• / SUBJECTIVE TYPE QUESTIONS . \; :a

•

"'~z~~~"'"'I""'~>°'<;.; ,_ . _~;,· a:~k~ch)

-fi:~"'&'-~'~~Q , .,. , -,.
'' '' • ,, ., f •

I..PP*" •-~.. t"trN•,~... t _,,

, n~~nAD~•\~~- ~~~~- ·-
~d...." """1..-. .......a.,.Wli,a/·.~"""~ ll..ooil lQ,..... ....,.'-
..,,,. ~---: u.... ...~ - - .....:...:.......c......:.-....
1
· Q. t. Who discovered that force~ th~ cause of motion? . Ans. Henry Cavendish.
, ' l!il Q. S. What is the unit of ~avitational constant (G)?
, 1 · . ., . . . . · [ii] [QJ
Ans. Galileo Galilei. · · 2 1
Q. 2. . Who formulated the universal law of gravitation? Ans Th is Nm2 kf ·
, · 1 ·• · l!il , e unit of gravit ational constant
, •. :. · . . ,.
Q. 6. How is gravitation different from gravity? [QJ
1 . . . ; . . ',,

Ans. Sir Issacforce· Newton. - ' · ·

1 Ans. Gravitation is the force of attraction between
. Q. 3• . Which causes the things to fall toward s
the Earth 7 . l!il any two bodies while gravity refers to attraction
between any body and the Earth. . 1
· • ·, -· · · '-
1 Q. 7. Is the value of 'G' dependent n the mediutriil ll
°
Ans. Force due to gravitythe
Q. 4. Who found out
constant (G) 7
.
value ~- gravitationa
[W
l
Ans. i:.
sent between the two bodies 7 ~
 GRAVITATION (33!.
- a scalar or a
' What does a small value of G indicate 7 Q. lS. What kind of quantity is weight
[Q) [Qj
8· A sillall value of G indicates that th
£
a, or~e of
vector 7 1
µis- atavitational attraction between tw0 e ordinary Ans. Weight is a vector quantity.
tr • cts ·
Q. 16· Give the relation between mas
s and weight of a
·
sjied obJe IS a very weak force. 1 [QJ
GiV'e reas on for the stateme nt, "The val body.
· a, 9, is greater at the ~j8
than at the equ of g"
ueatot h~ W =~
wt 7
1
!Al
..--~,,.-,-~-....--.~- ~~~ a~ ~
-12015) Q. 17. How many Newtons are there in 1 kg-
1
~ pales the r~dius o~ ~e . .Earth is lesser n
tha.::, Ans. 9.8 Newton.
ace is the
ato t · ., . ,u J At what place on the Earth's surf
that at the equ Q. 18.
'
•• j "

s
1
J weight of a body maximum 7
[Qj

:u;•~:~~-;-£-'a':'!'!- 2015) I
. · · (CBSE Markin ·
1
O ;:. Ans. At the poles.
ace is the
At what place on the Earth's surf
a~: The unit of mass is kilogram (kg).
~ Q.1 9.
weight of a body minimum 7
[Q]
[g] 1
Q• . ean the mass of an object be zero 7 Ans. At the equator. t
11 If the mass of a body is 9.8 kg on the Ear
th, wha
1 Q. 20.
MJS· No, would be its mass on the Moon ?
!Al
ct be zero [A]
Q, lZ. Why cannot ~e mass of an obje 7
It will remain the same on the Moon, i.e., 9.8 kg.
ct can never be zero beeause mass Ans.
,.,4 Mass ofb"an obJe. th 1
rv-· inertia and the
· . of an o 1ect ts e measure of its
by the bod y. l force 7 [Q]
. substance contained 1
Q. 21. What is the nature of gravitationa
a body 7 [g] ctive in nature.
Q. 13. What do you me ~ by weight of Ans. Gravitational force is always attra 1
whi ch b d
AJIJ· Weight of a body is the force with 0
y1
is at!J'acted tow ards the cen tre of the E~ weightl essness 7 [Q]
· Q. 22. When does an object show
Q. 14. Writ~ the SI uni t of wei ght Ans. Weightlessness is a state wh en
an object does
· [g] (Board Term I 2015) not weigh anything. It occurs only
wh en a
ton (N). ' 1 effect_ of
}JJS, SI unit of weight is New body is in a state of free fall und er the
1

E~~~~,.~~~~~~~~n:~.~ ~~~~~i~.~~
lf>J
~·:r:·: .. -• - ~ ..... -.,,.,,....,---~--- --- -. ., ,
1
only gravity.

.- ,._. .. .. ,,.-.,.~-.. ~-··~~~~~~

Q. 1. . Name the positions on Earth whe
'g is (i) maximum (ii)
,
minimu
re the value of
m? Justify your r.,i;: ~phv~ba&-~th-~ t
_building at the same time. They will
~'b ;on i'a tall
reach,the
ball s are at
. .~w ~r. · , .ground at the same time. Both the
• . IU+AI (Board Term-I 2014)
free fall ~d their initial velocity is
~e , ~ is
M value of ·at k sandJ
g; ·~ um gt2.J : '. . ~' .
s :di us ofl .~· . zero. (You kn ~,that s = ½
•• at the equator. At pole _the ~df
So the only ~y ~t they touch

.
ii less so value of g is more, at equator
of :Earth· is more so value of g is
V(R2). • . .: ·, ..·
·
.
less
J ' th
at e same time JS that acce
for !'<>th the balls. This ~ e n
lera
t
tion
pro
dun ng free fall every object accelera , .•
· same rate, irrespective ofit s mass. · .
JS
ves
same
tha t
te at the
. ·, ..
CBSE ~~ '.! '.! ! !1_!4) (1+1)
orcebe tweentwo . ~~e
-:...--- ~-~--P• - 2ot4)2
Q.2 . Explainwhathappenstothef Q 4 An - --:
objects if: (i) the mas s of one obje ct is doubled? ut earned a pot containing soil
(ii) the distanc e between the objects is tripled. 60 N from the Earth to the surface of
a~trgona
· • wei. ghin
re return
Moon. He kept it there and just befo

.;-,. J
~ (ODE 2014) d the soil
·•·•1 journey from Moon to Earth h~ weighe tha t it
·-.v 1--- -·'.' ""-~ ·# ~--... ~ nd
there on the surface of Moon and fou
the soil go
was only 10 N. Where did the_rest of?
and how much mas s of soil was lost
p~~ twice. 2 .
(gEuth = 10 ms- H8Moon = SEartb / 6)
F becomesone-ninth.
r•·-._._.-~~_:..__. ·
[Al (DDE-2014)
...:.. ~ -~L (l +·1 .
Given that, tii";~gh~ ~soil onM k (JON']J
· · ;·_:..__ .. ~ ....:
Q. 3· Explain an activity to shqw that
, during a free L Ana. ,.
accelerate at the - -S ~..::.,-~ ~~-
fall heav ier and lighter objects
IC] (Board Term -I, 2014)
same rate. I • o
 . . SCIENCE, Class-IX
Oswaal CBSE Question Bank Chapterwise & Topicwise, . sunultaneously dropped fro
I
another sto~egh~ Which stone would reach th~
60 the same h:~d why? [§ (N~RT Exemplar
Mass on the Earth, m1 == - == 6 kg ground fitS . take the same time to reach thl
Both stones ~ the two stones fall from th:
10
Ans.
Weight of the-soil on Moon == 10 N ground beca d accelerate due to gravity alon
Smoon =~ =10 ms-2 same height ~ }lave zero vertical velocity e.
6 6 Bot~ obje~ey are released. at
10x6 the inStan _1,....., are dropped from 1-.._
Mass on Moon, m2 == - - == 6 kg Q. 9. Identic·d ~~- One above the equator and ~o th
10 aeroplanes. the north pole, both from the &ante
Because m1 = 1'12, hence there has been no other above nting all conditions are identtca: ,
loss in mass of the soil on the surface of Moon height. Assu ckets take same time to reach th'
and decrease in weight was due to difference in will those P~ Justify your answer. e
the~vity. (CBSE Marl<!!tg Scheme, 2014) 2 surface of E . 'A1 (NCERT E
Q.5. Account for the following :
U1J xemp1ar1
f ,,., at the equator of the Earth .
The value o b
(i) On Moon, man feels lighter than Earth • Ans. an that at poles. Therefo_re, the packet fallsIS
(ii) Mass is scalar while weight is a vector ~~~~ at equator ~ comp~n ~o the poles.
quantity. the packet will remain m au for longer
~ (Board Term-I, 2016)
Thus~
timetnterval, when it is dropped at the equator.
The weight of any person on the M'?°n is about
(i) Pue to less gr,avitational force exerted by Q. 10. 1/6 tunes that on the Earth, 1:fe can lift a mass of
,Moon on man. • the Earth, What will be the maximtun
15
(ff) Mass do not have direction while weight kg ~hich can be lifted by the same force
has direction.· :;tied by the person on the Moon?
(CBSE Matking Scheme, 2()16) [A] [NCERT Exemplar]
1
Q.6. A stone and the Earth attract each other with an = gandgm = 6
Ans. &
equal and opposite force. Why then we see only
the stone falling towards the Earth but not the Force applied to lift a mass of 15 kg at the Earth,
Earth rising towards the stone? f=m&=15&N
~ (Board Term-12016) Therefore, the mass lifted by the same force on
the Moon.
e mass of a stone is very sm 15g
gravitational force produc
n inJt.' pue to very large mass m=.£_= K. =90kg
e yavitational force produces gm 6
leraf;ion ih · · Q.11. Suppose gravity of Earth suddenly becomes
CBSE Mar e, 2016) 2 zero, then in which direction will the Moon
Q. 7. · What is the source of centripetal force that a begin to move if no other celestial body affects
, planet requires to revolve around the Sun? On it?
;wh.a~ factors does tha~ force depend? [UJ [NCERT Exemplar]
. . .[U] [NCERT Exemplar] Ans. The Moon will begin to move in a straight line
. J\ns, .-Gravitational force. This force depends on the in the direction in which it was moving at that
product of the masses of the planet sun and the instant because the circular motion of Moon
,·. inverse of square of distance between them. is due to centripetal force provided by the
, '.·Q. 8. On the .Earth, a stone is thrown from a height in gravitational force of Earth.
.-~ direction parallel to the Earth's surface while

lfi~nAu".er
. Q. 1. Explain :
Type Questions-II (3mczrbl(lch)

where F is the force between two mas.ses m

(i) Universal gravitational constant
and M at a distance r apart. The numerical
. (ii) Free fall [QI (Board Term-I, 2015) 2kg-
value of G is equal to 6.673 x 10-11 Nm
Ans. (i) Universal gravitational constant is the 2
constant 'G' appearing in Newton's law of • The value of G was found out by HeruY
gravitation. Cavendish (1731-1810) by using a sensitive
F= GMm balance.
2 I
r (ii) Free fall : Whenever objects fall towafds
the Earth under the gravitational ~
alone, we can say that the objects are
I GRAVITATION

~ee fall ..~ e falling there is no change Q. 5. Give reasons :

10 th
e dtrection of motion of the objects.
But due t_o Earth's attraction, there will be (i) A piece of paper takes much long~ to fall
a change m the magnitude of the velocity than a stone through the same diStmce,
(1½ + 1½) . . when both are dropped simultaneously
2 sta from roof.
Q. • te lhe universal law of gravitation. Mention
four phenomena which can be ~ined by this (ii) The mass is constant everywhere the
law. 11!:!:A] (DOE 2017) weight keeps changing.
___,__,~.,., . ---~------.. (Board Term-I, 2015) (iii) The value of'g keeps changing as we move
~ · Ans. Universal~ ofG ~Ti;f;t0 SAQ-WQ:1 away &om the Earth whereas value of 'G'
t. ·. :· . ~~) _'lll~f~rc~}~t3;tbin~-~}~~.,:_ ,.· (_
·¥--~~
remains constant all over the universe.
:
~. . .. _ , (u) The _motion of the Moon around the Earth. [Al (Board Term-I, 2016)
I- ....
t ./
(iii) The moti~ o~ p~~ts.~ d th~ sun. · .
>:-': (iv) ._The_tid~ due .t o the,Moon and the~ .~
~ ~ , . . , ~ .(~BSE ~~.. ~ Scheme 2015) 3l
Detailed Answer:
~~..~ · - ---·--·•. -~......
.! ._
r -~ - ·a)-Thisis'~ ~j~
_. ~ha&orel ~~~to-~ ~
es5 IIIUlclU: area.
. .
:.
.
,• , , :
... . .
: ·. : . (ii) Because a~on.du6to ~
Universal law of gravitation states that the force l . ·. from place top~: . .:__,:_· ~- , ·. . .... .
of attraction between two objects is proportional
to the product of their masses and inversely
[ , . , . · (iii) · The value o{ g ~ ~ tittibide ·of ·
proportional to the square of the distance
. . .place and the mass
of the EarlJi: whle, .
between them. - is called universal constant as 1ts value
remains constant at" an the ~ In thd
Four phenomena which can be explained by this universe - ·· · .. ·· '.·, ·• ·· '-:.-: · : ~ ,· .. ·:~·j
,; ,: :. '. : 1cs'SE ~ Scheme,-~§'1\t,~j
law are:
(i) The force that binds us to Earth.
Q. 6. In which direction do the following forces act
(ii) The motion of the Moon around the Earth. when an object is in motion :
(iii) The motion of planets around the sun. (i) Frictional force
(iv) The tides due to the Moon and the sun. (ii) Gravitational force
Q.3. In which direction do the following forces act
(iii) Cenhipetal force [g] (Board Term-I, 2014)
when an object is in motion ? Explain with the ,...,.......,,.,.,.._ _ _ - ,, :r ,._ , , ••, . ~• .
help of an example. ·. Ans. (i) Opposite to"the direction of motion. . .. : ·~
(i) Frictional force . ~.. .(ii) ~wank-....... ·. :'. ·_' ·.: /. . . .-·
(ii) Gravitational force
. . flii) 'lbwardsthecentre -·., .·. .-.":·:\, ~ .+·t _+l
~ · · ; 4, > .P•':'"ift!'"J . •
IU+AI (Board Term-I, 2015)
.g:-, 'f' , : , ~ ~ •. ~
.-· ., .. •_.· . esE · . ~ .• 2014
··:; AnL f (i) J:rictional force:f~~cltjvaids ;: ... ':' :: . Q. 7. State universal law of Gravitation. Derive an
:·.~('.'.,~?'.· _:; .bple : H a book
slides· across the expression for gravitational force between two
<·_,.. ·r :·': · surface of a desk, then the desk exerts a bodies. [g] (Board Term-I 2014) (NCT-2014)
-:t<·\ · -: - / &ictiorial
... y ~ I- • ~ • , ,
force in opposite (i.e;,
·· •· :' ..'. :' , direction of its motion.
'.
·
backwards)
' • .
. ,. .-. . -~-·~. . .- ,.~. .,. ,.-.-,.:!""'<II~--~
· (DDE2014)
. .
/.,
I
///- (ii}' • G~vitatio~al
,...~. • ,• .,, • •
force : Downwards
· ~- ;'·;:.-~_,; Example:Whenwethrowa~intheail;·
, "'~ ~ ,. . ' und. .·
.
,:·,
[, Ans. Universal law of gra~tion stata
-of. ~
;.. ;.. i
l:betweel\ ~
! propottioaal .to tt.·
'p • , • , ·': ,it returns to the gro · . - ·· :
:_,/;· ._; :: ': (CBSE Mar~g Scheme, ~ J !¾ + 1¾)
. . . : . : ~ ~ - -• ~1-oo<....___ ----~.-...._..-.....
Q. 4. A man's weight when taken at the poles is
---~ t, . Letthetwo~ •
·• · · · anct.in-vetsely
. ' :.' : distance between

600 N. Will his weight remain the same when ·. and 'r,(
measured at the equator ? Will there be an ! distance
increase or decrease in his ·weight ? Explain.
[Al (Board Term-I, 2015)
Ans. N~, his weight will not remain same as that at the
poles. There will be a decrease in his ~eight at ·
the equator. As the radius of the Earth mcreases
from the poles to the equator, the value of 'g
becomes greater at poles decreasing towards
equator. Also, the force of gravity decreases from
poles to the equator. 3
 ~
■-r-~--,-..,,__......,__,
-~~~] __,-.,.._.,. ,. ,
Oswaal CBSE Question Bank Chapterwise & Topicwise, SCIENCE, Class-IX
It
l
·••-•r•-•·- - -
So, from Newton's second law, ~
J:;,. .,.. : is·~;~{~;,;~~--;;~~ti~n""~~;;Wrt)
Where 'G'
· F =mg
.I

~e,•... · · . ·, The numerical value of G = 6.67 x 10-11 Nm2 Kg-~ From equations (i) and (ii), we get ··-(il)
b..,.,~ ,,,.,,_,,,,;.,...,. ,..,·-,,.1.-.~c..(QJS.~ ~arking _S cheme, 2014) (1 + 2). . GMm
Q. 8. Wha~ h~ppens to the magnitude ·of the fo;~; ;f mg=-;,-
· gravitation between two objects if : lij]] GM t
(i) mass of one of the objects is tripled 7 or, g =7 ... i
···(ill) l
I
(ii) distance between the objects is doubled 7
(iii) mass of both objects is doubled 7
This equation gives acceleration due to ?1"aVi.ty !
at points far away from the Earth. Now, if bod f
[QI (ODE 2014) is located on the surface of the Earth, then r ; t
Ans. The force between two objects is given by R, i.e., the radius of the Earth. Then equation (iii) j
'Universal gravitation law'. It is numerically becomes I
stated as,
F = G (m m 1 2 ) .
&umce = C: \
\
d2 This ~quation gives acceleration due to gravity at \
(i) Mass of one object is tripled : the surface of the Earth. i
The value of'g on the Earth's surface is 9.8 ms-2 j
F =· G (3m,)m 2 · -1
d2 , . ; (1 + 2) '
Q. 10. Find the weight of an object at a height 6400 '
F = 3G(m,mJ km above the Earth's surface. The weight of the ;
. d2
object at the surface of the Earth is 20N and the ¾
Force will be tripled. radius of the Earth is 6,400 km. [A] (Board 1
(ii) Distance between the objects is doubled : Term-I, 2016) ----
; : " ~ /........,~'f,,''"'"'>_,.•••-•,!' ~ -....v••-•"-r"' .•~•~~- .~ ~
i
F _ G(m1 m2 ) .. t{· ·Ans. ,w ~ ~g = ~N . ,·. ;.
- 2
(2d) .. ·, , , . f:,:• i .· Mass = 20 ,.;, 2.04 kg g=R2
GMe
e
F = G(m,m2 )
· 4d2
···· '.

.ft;''"•/;_:[
f::..: "'· ,_-, · .: ··
Re
{Re+H)2
]
2

fi:"'- ;.,~·-< ; ';_C'. > ~ ••

C . 2 ·
~ ··..
Force will reduce to one-fourth of its previous
value. r = 20 X (6400) = 20x.!.
(12800}2 4 =5N
(iii) Masses of both objects are doubled: Lu.,~, . .,._ .· .. . (CBSE Marking Scheme, 2016) 3 '
· F ::: G{(2m,)(2m2 ) } Q.11. ~1~1:~;:ctivity. to show that, during a free•
. . ' d2
fall heavier and lighter objects accelerate at the
F ·=· 4G{m m 1 2}
same rate. ID] (Board Term-I, 2016)_'
ft'. .. •- •";·•~·~-·· .. .,..;.~,._.•'!'.~-- .'· . . ·".,.--'· ..,. •· ~--' . ~-~ ,' w.. - • "
d2 ~ · Ans. Drop two balls with different mass from a tall ·
· Force will be four times greater than its previous i· ·.
building at the same time. They will reach the ;
value. (1 + 1 + 1) t . . ground at the same time. Both the balls are at ;
Q. 9. What is meant by acceleration due to gravity ? ;· free fall and their initial velocity is same that ,
Derive an expression for acceleration due to ~ . is zero. As you know that, s .= ¼ at2, so the l
gravity in terms of mass M of Earth and its l· only way that they touch the ground at the
radius R. [D] (DDE 2017) L same time is that acceleration is same for both
Ans. The acceleration produced in the motion of a t· .
the balls. This experiment proves that during
. body falling freely under. the force of gravity is t, ·1 .,. , .. free . fall objects accelerate at the same rate,
•:.-.
. called acceleration due to gravity: It is denoted
by'g'. ·. .
t·. . : . ' irrespective of their mass. . > • •

Consider the Earth to be a sphere of mass M and L.'"--,::.:.,;~._,::L;,;".. ,::_~~:.,.~.: J ~~E ~ ~ g-~che~~ ~~) 3
radius.R. S:uppose a body of mass m situated at ..- ' Q. 12. Write a mathematical expression for th
distance r from the centre of the Earth. universal law of gravitation between tw
' ' ' · : 'As we know, according to Newton;s of iaw bodies of masses m 1 and ~ placed at a distanc
'd' from each other. If this law is true then wb1.
' . ~ gravitation, the for~e ·o_f attraction between the
. '.' .· Earth and the body ts given by . we do not find any two objects in a room n,ov&
F = GmM !r2 ...(i) towards each other due to this force ?
This force produces an acceleration 'g, called (G = 6.67 x 10-11 Nm2 kg-2)
acceleration due to gravity in the body of ~ (Board Tenn-I, 20161
massm.
 GRAvrr~
•A:rJON
.-,....c~
G~i'.
and -weight.
~~
""'" ·-·-
,~...,....~~·---
,·
.....
- 'jl Q.16. (i) Differentiate between inass . t equal to
~ ~etat
l (ii) The weight of a body ~t ,.rill be
1Blll (' , · the radius of the Earth 15 N · tJttee tiJneS
' 11 2 -2 · its weight at a height equal to
. 6,67 >< 10- m kg .
c;- gravitational const~t is extremelt small the radius of the Earth? 1 2016)
11": . an ·0 rder of magrutude of 1o<- t). For ~ (Boar~~
wl~ in a. room, mass ~as an ?rder of 2 in
'll~artitude, 1.e., 1D2 kg while for distance it is at i .~;,-~-(i) ~ is th;~~~-!;1:
the ~: i
l
weight is force with whi
1
_:;ft,i.e., 101 m. . . ; , , .
the order of magnitude of the gravitational l rI attracted :i;; i by F,arth. . .
fbUS iS 10-1.1 X ~Q2 X 1lJ2/(10 X 10),
9
which
. fO!C:rder ,of magni~de of 1(,, , .~hich shows
givej' . Mass is constant at all places ,

I
. . . fro place to l
8l'at th~ forc.e is ex~_emely small. . ., · . · Weight keeps on changang IJl . j
~~ (CBSE Marking Scheme, 2016) 3
~
• 1 " ·
µ ~ . . r . _ . . . , . . . , . _ _ ........ _ . . . ..........._........<E...
f place. M

II
· solid objects of masses 1 kg and 2 kg are
,13· :,°pped from a helicopter at the same time. (ii) g-
.- G d2
0 W}tich one will reach the ground earlier ?
Justify your answer with suitable reason. :, when, d' e' 3d M GM l
= ~ x (3d)~ '== 9d2 -
'1 t . .
~ (Board Term-I, 2016)
l
l
Then, . g'
· Boih~~~~~~~i~~ s~e~e. •,
~ ·'fhis''is ~cause~.'g, i.e., the acc;eleration due1
.~ ~Jl?. gray!~ ~cti?g on. a_b?dy is in~ependent o~.,
I . Or ' ii_- ~' •. -. : .
_ .:. its l;llass..Hence all bodiell fall with the 2same i•· ,· · Original Weight,= N = ~: . N~· N · .... · 1·

.' velocity an<,l acceleraµon, which is 9:8 _ms- • •. Weight,= N' = mx9 or =. 9 ....3
•..(CBS~__Marking Scheme,!9~613
... ·., .. · :
Q. l , 'Jbe gravitational force between two objects is
4 100 N. How should the distance between these
..-._IS!~~ ~~ 0 th
, Q. 17. The weight of a body on the surface ~ e Earth
is 392 N . What will be the weight of this body on
object be changed so that the force between th
a planet whose mass is double that of e Earth
them becomes 50 N ? !Al (Board Term-I, 2016)
and radius is four times that of the Earth-
~ H~re F1 =100 N ' I½":: 50 N~ ~ ._ [A] (Board Tenn-I, 2014)
_,.,.,,...,--·~~~~c--..-..•..,-iT"~~
If, r is the original distance and r2 is1the distance
1 .
,- · between ~e two objects, then
' -
Fa::-i . ~ _'. ; Ans:-~et th;;;;; ~~- ~;-~ ~ '~'·and.its.~ ~i
r be'R' . . ,, ... ,.•. !•,.:.·. -t
,..
. . :, ~
I
)" -~ ~ .~
~
,. • , ·, ·.' · · 2 l
. . · '
.,. , .

. · F1 , . ( tz)
2

100 . ., .
Then the acc. due to gravitx (g) GM/R: = =
2 ?·8 m!s2 where G _is the Gravitati~ ~ o ~ t _'J
;tli~. = 50 = ' . 1 t' · Mass of the planet = 2M · \ ·.. ~
. J,, the <futance between the objects should be ll
i ., maeased to ,.Ji times. - · · . ·: . . · ' : 1
I ,. -. . . Radi~-of the planet= 4R · - .. , . ·
Hence, acc. due to gravity on that_planet
· _I
J
(g') = G(2MY(4R)2 ~
'' •,·',,..,.:: •.~(£!~.~M!~~~~~
,

Q.15. The mass of sun is 2 x 1o3° kg and that of Earth i .' ' ' . ·=: 2GW1~2
is 6 x 1o24 kg. If the average distance between • = us (GM/R2>
8
the sun and the Earth be 1.5 x 10 km, calculate = 1/8 X 9.8 = 1.225 'm/s2
the force of gravitation between them. (Take Weight of the body on Earth.= 392 N
G = 6.7 X 10-11 Nm2 kg- )
,
2
IA] (Board Term-I, 2016) .. i:f~n~,.its mass will be ~w1-s>.':"' _40_kg . , l
' l ! ' l " " l ' ~ i r-;,;,,..:u,vr; -~-~~ ¥"":-l""__....,,...
. So, its weigh~ _on that particular p~et will be l
= GM1 M, · .. ,. (40 X 1.22.5)- 49N . , , .' ., .., . · i
... dl
. ~ Write
----~--~-~-~·_J?S~Mar~~ ~ _!l~_!~~
--:.-- - - - ~~- -
6.7x10-11 x2xi~ x6x10
(1.5x1011)2
26
Q. 18. ~ee differences between gravitational
acceleration (g) and gravitational constant (G).
• 3.57 X 1022N . . (!µ} (g] (NCT-2014)
..__ .·
--.--...--
· (CBSE Marki!,tg Scheme, 2016) 3
...~-.---~ .. --·
"i' '~fl
Ans.
Oswaal CBSE Question Bank Chapterwise & Topicwise, SCIENCE, Class-IX
o-(49)2 == 2 x (-9.8) X h

S:, . ~ due ti, ~gruilallooal h = (:) m =122.5 tn

lI
~~• . ~ · :; gravity, (g) . ·· ,. constant (G) ~
(i) Acceleration due Gravitational constant
(ii) Tune taken to reach the maximum height, t
V ==u+gt
i
to gravity is the is numerically equal to
acceleration acquired the force of attraction t == (- 49)/(- ~-8) j
by a body due to the between two masses of [As final veloaty, v = 0 m/s] ::; 5
s!
1
Earth's gravitational 1 kg that are separated . ame time is taken to reach the ground
pull onit. by a distance of 1 m. Smee, s . ,
from the maximum height.
(ii) g is a vector quantity. G is a scalar quantity. So, total time taken to return to the ground
(ill) It is different at =(2XS)s=10s
The 'G' is a universal
different places on the constant i.e., its value is Wh t is the magnitude of the gravitationai .
Q.20. for;
surface of the Earth. Its same (i.e., 6.7 x 10-11 N between the Earth and a 1 kg object on its 1
value also varies from m2 kg-2) everywhere in 8
urface ? <ME = 6 X ta24 kg and RE = 6.4 X106 Ill) 1
one celestial body to the universe. . (NCER~
another. %radiusoftheplanet = 6.4 x to6 m
Ans.
(1 X 3) ME = mass of the planet
Q. 19. A ball is thrown vertically upwards with a = 6 X toZ4kg
velocity of 49 m/s. Calculate : G = Universal Gravitational Constant
(i) The maximum height to which it reaches.
= 6.67 X 10-11 Nm2/kg2
m =mass of the object = 1kg i
(ii) The total time it takes to return to the According to Newton's Law of gravitation, the
surface of the Earth. , IA! (DDE-2014) gravitation force (F) is i
Ans. Initial velocity of the ball (u) = 49 m/s F =GMEnv'Ri ½i
Final velocity of the ball (v) = 0 m/s 24 I
6.67 X 10-ll X 6 X 10 X1 t
Accel~ration for up~ard motion (a) = - 9.8 m/s2 F = 6
2 2
(6.4x10 )
- '' (i) Maximum height reached by the ball = h
. - · _... v2~u2 =2 h · .. ,,. · · F =9.8N
: ' .' '· ' .
'?iilf:iA;;"i""'.f;,,\'.}
. ~ . . . ,_ ·'.. ..:__.f.-!._~·~F""'_
/
•· _,,,11"1""_._•►,..w.,,_>_NNt!"_·~---.""'
,,..
1J·~'4'.:t'ii'1'~~-.o:~;,~'~t•(.i,:•'.Y..P:-~>,i(''i,,;~
. .

,.
.
~•.~ "·.'_' '"_'
.
"'·'" ' .... ,~,, ....,....
,· ','.• · ·,._.,: · ·' . .,
·~--,- - •
· .
'Aziswer,TY.Peauestions~~-·/(::!,(//· :;:·, ·...... '. (S _marlcseach) i i
,;·!,"-"\l' ;'-""'"o,,·,,,,/> .,,-,.; •:•'·"'

..,,,,,,}fu;<w,:,'{f·';,t:.,.~d:Waetf<s-":f,%¥<;'.).•>;,,;.",41.ij!'•:w\'.,Ji·.' . .,-., • · i '

>• • ••• -;,. ➔" · * .............. · ,,, · •
Q. 1. (i) ·Abar of metal has amass 200 gand a certain :/-:>.<.\\~ 112 Nis ~cigh~;;,;;ut on M~ J !
weight. Mass remains th~ same when _:, ::.'.' Themassofabodyisconstanteverywhereinthel 1
weighed at ·equator but weight decreases. ·. ._ :.. · ·: universe~So, the mass of the astronaut would t
Why ? ·. ·., ··.·. be same on the Earth as well as on the Moon I
(ii) Differentiate between. mass and weight. -~ .- ~ '. 0: _l~.; 70 ~ . . .· : .. . - · ,. ..vv..4 '
Write any three ~erences. . . · • -~.,.. .~, (CBSI Mar~-~ ~~ ~~ 6) (~ ~
[A] (Board Term-I, 2016) Q. 3. (i) Prove that if the Earth attracts two bodies .
--~='!1>"!'1·.,,.......~.._,....,..,,.,..1;i:r.---.!l!'""'"'-:-" "'...,. placed at the same distance from the
· dent , on gravitatim,w centre of Earth, with equal force; then their .
, ~~ masses will be th~ sam~. ~
~ ·..: i (ii) Mathematically express the acceleration
· • due to gravity that is expressed by a free
falling object.
(ill) Why is 'G' called a universal constant 1
·. .Q.,4 , ~i;i~e,.thr4:e point$ ~f ~e.rences.between mass . __ ~ [Q] (Boa~d Term-I 20l ) 4
' · · ' and weight How much would a 70 kg astronaut ~-~""'"~-~•-·:--- ----:"'.
weigh ,on ~o~~? What' would be his mass on ~·•::·.'f~r; :., ·-~~,. &st ~y be m1
·' • .' ' ·· the'Earth- and on the Moon? · · body be m1 .
. '. ' ' ' . ' · . IU+AI (Board Term-12016, 15) )o~ <)n 2nd body
.. ,. ,; ·. ,

M and M cancel and

· - ~ ~........i...w~~- • . - ---
 ,
►
_ _,",;~--~ -..---..... .... - ·~ ~ ......__
GRAVTJ'ATION ~
. . . This leaves --~--- .,.....,., Earth. If the value of 'g on Earth is 9.sms-z.
· m1 =mz Calculate.
.: . .H~ce proved. (i) 'g on Moon.
~il) · , : g = GM1R2 (ii) Mass of person on Moon
(iii) Its value is constant in the uni (iii) Weight of person on Earth
.. .<~~E_M_arldng Scheme,2014 ;~ 1 + 1) (b) How does the value of g on the Earth is
1..-........--..,.;..•~_..... . , . ~ . a.1W.L..c.~....~41;u.,;...,. • • related to the mass of the Earth and its radius?
Q.4. (a) Write the formula to find
gravitational force betw
ili. . ._ ~·-. Derive it.
e magrutude of !A+UI (Board Term-I, 2015)
. een the Earth and

~-•~ )
obJect on the Earths' surface. an
(b) Derive how does the value Of . .
force 'F' change between tw graVItational
the : 0 0 b'
(i) gooMoon=-X¼~9B:; ;.,.-,1
Jects when • I

· (i) distance between them . d (ii) Mass·~ ~ n ~ ! ·:.;. ·1lO.S4 =68 kg ·1

half, and is re uced to .
. . . g · · · 1.63 ·. · l
(ii) mass of one object is . _: ~ -mg. ~-~ -x 9.s'l
· (iii) ~eight on Earfu
tim ~ mcreased four
-~,_.,..,., ,t.~:. · . = 666.4N. . , . · · :.· . · , 1
-;...,.,_"'I'~ ~~_::d Term-I 2016) t. "" (b)Derivationo fg=GM/R2 ·•: .... ,·.· .' · ~
,J".; (afi~ ;•;,G ~ ,i · .· t .; · · , . : : .:'., , . .
~---- : eh ,......1,~ g ~~~I ~1..~J
_...,-,-.._..c ! '·-1 R~,
• ..-:.~, ' • ~ · . . ( r«, ✓ •. - " •

. ·"' _·\ ~)-t (i);According to the law of ~~ti · · th Detailed Answer :

,g
· r· a

~;, ,;e:.-.':':.;~--:<+•··~> .. ,force of ttr . . . . . on,

;, f\/i .. . . . a. action .acting between twoe (a) (i) gF.arthx .!. = 9.8 x .!. = 1.63 ms-2
. , :\):\~·\.~es ~ gi.venby, i :., . .•...: 6 6
;. f;
....• . . . . . . GM ~,. .. ?
. ' '- M1
• ~
.•. \ • .,., (ii) Mass on Moon will be constant and does
· , N,..,.~:- ···i'F1· ·· 1m2 "' G ~ •· ,,, not change from place to place. Hence,
"' ~ ,-~-·
i.- '.,, ;.
............
~f-
2.··~;,
.·_·1:·::_-~,.•\~: " · R......
•
,;:::'" ~~ 2 .,
•
''\ . • :>,
.,. ,,
...,"' . . 1 • ... ' .; : :· ••, ...
(R)
- - ""'~,.,.
mass of the person on Moon will be 68 kg.
-
'~ \"~-·",., t..r, . , , t ~
~. , -;., • , . . , ,, ;,.i' i' ,l , ,~~ 2 r- '~ (iii) Weight on Earth = 68 x 9.8 = 666.4 N.
• ,Y -- . :.t- , :,'{ •
. ., ·· · ·
: s ' ,.
, ·• 1
= 4G Mm
R~
"•,,t"
::::: '4F·
r., ,,,
~
?' :,
0

,~.;1;..· ~--!-
(b) According to Newton's law of gravitation,
: ,··t~
the force of attraction between Earth and a
, • ...... . . ... • ,, _...,.· -~ . 1 ..- ,_:3~ ., · - -,,,. ·• '.

th~·; ¥;~J::t~~~-
.,<•~ - .•:t •

J•' ·.":Thus, , when·

1 body is given by
,' ~ r / _the objects is . retiuced . to· half , the GmM
... (i}
F=~
. '.:, ·/ &1'8-vitatio~ _force ' incrJ~. by~four
• :.f. r• . .7-~ the ongmal force. . . . ' •·
, , , , , , Force produces an acceleration . 'g. So, from
... · 'F'_= GM X 4m/R2 =4F , . Newton's second law F = mg .... (ii)
t ; ' . 'f • • 4,: , . . . ., , . . .. ' ' '
...:. ~! as the mass of _any one of the object From equation (i) and (ii) we get . '.
,, .; ~ ,. ~ mcreased four times, the force is also
.>.: :·:;
increased by four times. ) .
GmM
mg=. - ,2-
a:mi~~'.;....::...:~:i_CBSE Ma_!..~_~ em~ 201.!)J.3...! 2)
GM
Q. 5. (a) A person weighs 110.84 N on Moon, whose g =,2
-
acceleration due to gravity is 1/6 of that

, , CASE BASED QUESTIONS -~ .

(D)At the south pole

~~a~~~~=~=~~=~]
I. Read the following paragraph and choose the
,Ans. Option (A) is correct.
(2) Which of the following stateme~t is true?
(A) The frien<t' at equator. will' agree 'with ' the
correct options to answer any four questions
given below: · . . weight o~ gold bought at poles. . · ..
· ·
Amit buys few grams of gold at the poles as per (B) The friend a~ equatQr will not agr~ with the
the instruction of one of his friends. He hands . weight of gold bought at poles. .
over the same when he meets him at the equator. .(_C) The fri~nds at the p~les will not agree with
(1) At what place on the ~arth's surface is the · the weight of gold boughtat poles. •· .' .°,
weight of a body minimum? (D)~e friends ~t equator as well as at the poles
(A) At the equator Will agree With the weight of gold bought at
poles. ·
(B) At all places the weight will be equal
Ans. Option (8) is correct.
(Q At the north pole
- ':"I
~ 44:--1J Oswaal
- . . SCIENCE Class-IX
CBSE Question Bank Chapterwise & Top1cwise, '
(2) What will happen if they are
. dr
opped
Ill
s!
.. : ·
hi l
(3) The value of g is greater at the poles than at the
equato1t so the weight of gold at the equator will
be
vacuum?
(A) The piece of paper
will touch the
grolln.<l
Il-
(A) more than the weight of gold at the poles. first
m both will touch the grolln..1 i1
(B) less than the weight of gold at the poles. (B) In vacuu \( l
. (C) same as the weight of gold at the poles. together. d fir lt
in will touch the groun st
(D)zero (C) ThNe coo£ them will touch the ground. '·
Ans. Option (B) is correct. (D) one
(4) What is the relation between mass and weight? Ans. 0 Pti.on (B) is correct.
f
_
ur answer.
(A) Weight (W) of the body is always less than
(3) Give reasons or yo . . !
(A) In case of air the resIStanC~ provided by the l
the mass of the body.
(B) Weight (W) of the body is same as that of the
air is less for paper than com. . t
mass of the body.
(B) No resistance is pro~ded by au.. j
(C) In case of air the resIStance ~rovided by the \
(C) Weight (W) of the body is inversely
. is more for paper than com. i
proportional to the mass of the body.
(D) Weight (W) of the body is directly (D)~ provides equal resistance for both the i
proportional to the mass of the body. objects~ · j
Ans. Option (D) is correct. Ans. Option (C) is correct. . ;
(5) What is the SI unit of Mass? (4) What is meant by free fall? {
(A)Watt (B) Newton (A) This is the fall of body when many forces I
(C) Kilogram (D) Pascal ·
are acting on it from all the sides. ~
Ans. Option (C) is correct. (B) This is the fall of the body from one medillll\ t
Il. Read the following paragraph and choose the to other. . i
correct options to answer the questions given (C) In this the body is prohibited from falling !
below: · down. t
Seema \;Vas standing on a terrace of a building. (D)The falling of a body from a height towards •
· She dropped a coin and a piece of ·paper Earth under the gravitational force of Earth
· simultaneously from the same height (with no other force acting on it) is called ;
_(1) _. Which of the two will touch the ground first ? free fall. !
· ;_, · (A) In air the coin will touch the ground first Ans. Option (D) is correct. '.
(B) The piece of paper will touch the ground (5) Which of the following statement is correct? i
first (A) In case of a free fall, there is no change in the ·
(C) Both will touch the ground simultaneously. direction of motion of the objects. 1
(D)None of them will touch the ground. (B) In case of a free fall, there is always a change ~
· Ans. Option (A) is correct. in the direction of motion of the objects. '.
(C) In case of a free fall, the direction of motion '
reverts. ·

Ans.
(D)None of the above statement is correct t
Option (A) is correct.
□□ -