practice questions : gravitation (cbse IX)

1. GRAVITATION
MULTIPLE CHOICE QUESTIONS
Choose the correct option:
1. Two objects of different masses falling freely near the surface of moon would
(a) have same velocities at any instant
(b) have different accelerations
(c) experience forces of same magnitude
(d) undergo a change in their inertia (a)
2. The value of acceleration due to gravity
(a) is same on equator and poles (c)is least on equator
(b) is least on poles (d) increases from pole to equator (c)
3. The gravitational force between two objects is F. If masses of both objects
are halved without changing distance between them, then the gravitational
force would become
(a) F/4 (b) F/2 (c) F (d) 2 F (a)
4. A boy is whirling a stone tied with a string in an horizontal circular path. If
the string breaks, the stone
(a) will continue to move in the circular path
(b) will move along a straight line towards the centre of the circular path
(c) will move along a straight line tangential to the circular path
(d) will move along a straight line perpendicular to the circular path away (c)
from the boy
5. An object is put one by one in three liquids having different densities. The
object floats with 1 2 3 , and 9 11 7 parts of their volumes outside the liquid
surface in liquids of densities d1, d2 and d3 respectively. Which of the
following statement is correct?
(a) d1> d2> d3
(b) d1> d2< d3
(c) d1< d2> d3
(d) d1< d2< d3 (c)
6. In the relation F = G M m/d2
, the quantity G
(a) depends on the value of g at the place of observation
(b) is used only when the earth is one of the two masses
(c) is greatest at the surface of the earth
(d) is universal constant of nature (d)
7. Law of gravitation gives the gravitational force between
(a) the earth and a point mass only (b) the earth and Sun only

2. (c) any two bodies having some mass (d) two charged bodies only
(c)
8. The value of quantity G in the law of gravitation
(a) depends on mass of earth only
(b) depends on radius of earth only
(c) depends on both mass and radius of earth
(d) is independent of mass and radius of the earth (d)
9. Two particles are placed at some distance. If the mass of each of the two
particles is doubled, keeping the distance between them unchanged, the
value of gravitational force between them will be
(a) 1/4 times (c)1/2 times
(b) 4 times (d) unchanged (b)
10. The atmosphere is held to the earth by
(a) gravity (c) clouds
(b) wind (d) earth’smagnetic field
(a)
11. The force of attraction between two unit point masses separated by a unit
distance is called
(a) gravitational potential (c)gravitational field
(b) acceleration due to gravity (d)universal gravitational constant (d)
12. The weight of an object at the centre of the earth of radius R is
(a) zero (c) R times the weight at the surface of the earth
(b) infinite (d) 1/R2 times the weight at surface of the earth (a)
13. An object weighs 10 N in air. When immersed fully in water, it weighs only
8 N. The weight of the liquid displaced by the object will be
(a) 2 N (b) 8N (c) 10 N (d) 12N (a)
14. A girl stands on a box having 60 cm length, 40 cm breadth and 20 cm
width in three ways. In which of the following cases, pressure exerted by
the brick will be
(a) maximum when length and breadth form the base
(b) maximum when breadth and width form the base
(c) maximum when width and length form the base
(d) the same in all the above three cases (b)
15. An apple falls from a tree because of gravitational attraction between the
earth and apple. If F1 is the magnitude of force exerted by the earth on the
apple and F2 is the magnitude of force exerted by apple on earth, then
(a) F1 is very much greater than F2
(b) F2 is very much greater than F1

3. (c) F1 is only a little greater than F2
(d) F1 and F2 are equal (d)
16. The gravitation force between two bodies varies with distance r as
a) 1/r b) 1/r²
c) r d) r² (b)
17. The earth attracts the moon with a gravitational force of 10²º N. Then the moon attracts
the earth with a gravitational force of
a) 10ˉ²º N b) 10² N
c) 10²º N d) 10¹º N (c)
18. The value of g at pole is
a) greater than the value at the equator (c) equal to the value at the equator
b) less than the value at the equator (d) none of the above (a)
19. A coin and feather are dropped together in a vacuum.
a) The coin will reach the ground first
b) The feather will reach the ground first
c) Both the bodies will reach the ground together
d) The feather will not fall down (c)
20 Newton’s law of gravitation is valid
a) on the earth only (c) in the laboratory only
b) on the moon only (d) every where (d)
21. The acceleration due to gravity is 9.8 m/s²
a) much above the earth’s surface (c) deep inside the earth
b) near the earth’s surface (d) at the centre of the earth (b)
22. When a body is thrown up the force of gravity is
a) in the upward direction (c) zero
b) in the downward direction (d) in the horizontal direction (b)
VERY SHORT ANSWER QUESTIONS
1. A body of mass 10 kg is taken to the centre of the earth. What will be its mass there?
Ans. 10kg
2. Write the units of ‘g’ and ‘G’.
Ans g---ms-2
; G----Nm2
kg-2
3. Define weight of a body.
Ans. Weight is the force by which the body is being pulled towards the centre of the earth.

4. 4. What will be the direction of acceleration due to gravity if the body is thrown vertically
upwards?
Ans. Downwards.
5. Why does a body weighs more at poles than at equator?
Ans As Rp<Re, so gp>ge hence Wp>We
6. State the factors on which up thrust or buoyant force depends.
Ans It depends on the nature of the fluid.
SHORT ANSWER TYPE QUESTIONS
1. Why are double tyres provided at the rear wheels of a truck?
Ans As pressure =1/Area, so more is the area of tyres lesser is the pressure exerted on the
road.
2. Two bodies A and B, having mass 50 kg and 100 kg respectively. They are dropped from
a certain height simultaneously. Which body will reach first on earth surface? Why?
Ans Both will reach the earth surface at the same time, as ‘g’ is independent of mass of the
object.
3. There are two kinds of balances i.e., a beam balance and a spring balance. If both the
balances give the same measure of a given body on the surface of the earth, will they give
the same measure on surface of the moon ? Explain.
Ans. No, they will not give the same measure, as the g on moon is 1/6th
to that on earth so
weight on moon is 1/6th
to that on earth.(W=mg)

5. Across: 5. Gravitational Constant, 6.Tangent, 7.centripetal force
Down: 1. Weight, 2. Gravity, 3. Mass, 4. Gravitational Force.

6. NUMERICAL QUESTIONS
1. The density of water is 1000 kg/m³ . If the relative density of iron is 7.874, then calculate
the density of iron .
Ans Density=R.D x Dw so D=7.874 x 1000=7874kg/m3
2. Find the acceleration due to gravity on a planet whose mass is twice and radius is thrice
as that of earth .
Ans. gp = 2/9 ge
3. Suppose an astronaut lands on the surface of moon and drops an object from a height of
‘h’ from the surface. Find ‘h’ if the object takes 3s to reach the moon’s surface .
Ans h= ut+1/2gmt2
= 0+1/2x9.8/6x32
= 7.35m
Worksheet #2
Topic : Newton’s law of gravitation
Assessment Technique :Sorting out based worksheet
Assessment parameters :1 mark for each correct abacus bead
Assessment time: 10 min
Instructions :-Some information about gravitational force, acceleration due to
Gravity and gravitational constant is given in the box.
Match the given information with the above mentioned quantities
By filling the correct number in corresponding abacus column
Some information may match with more than one abacus column
1 GMm/R2
2 Same for all objects on the moon
3 Depends on the mass of the object

7. 4 Henery Cavendish
5 9.8 m/s2
at the surface of the earth
6 Newton
7 6.673 x 10-11
Nm2
/kg2
8 Decreases with increase in height
9 Remains same all over the universe
10 Directly proportional to the product of masses of the two objects
10
8
9 8 6
7 5 3
4 2 1
TOPIC - Gravitational Force
G g F