Gravitation Class 9 Extra Questions and Answers Keralla Syllabus Physics Chapter 4

The comprehensive approach in Kerala Syllabus 9th Standard Physics Notes Pdf Chapter 4 Gravitation Notes Extra Questions and Answers ensures conceptual clarity.

Kerala Syllabus Std 9 Physics Chapter 4 Gravitation Extra Questions and Answers

Question 1.
Complete the following

Answer:
(a) 15; (b) 20; (c) 10

Question 2.
Correct the following.
a) Force of attraction increases when an object is raised from earth’s surface.
b) The force of attraction on the surface of the earth will be minimum at the polar regions and Maximum at the equatorial regions.
Answer:
a) Force of attraction increases when an object is raised from earth’s surface.
b) The force of attraction on the surface of the earth will be maximum at the polar regions and minimum at the equatorial regions.

Question 3.
A stone and a sheet of paper are dropped together. Do both of them reach the ground simultaneously? Why?
Answer:
No, paper falls slowly. This is due to air resistance

Question 4.
State true or false
a) The value of g will be the same everywhere on the earth.
b) The factors that influence the value of g are mass of the earth and radius of the earth.
Answer:
a) False
b) True

Question 5.
Classify the following into ‘mass’ and ‘weight’.
a) Unit is N
b) Measured by using spring balance
c) Unit is kg
d) Measured by using common balance
e) Does not change according to places
f) Its measurement is mg
g) Its value is O at the centre of the earth
Answer:
Mass
c) Unit is kg
d) Measured by using common balance
e) Does not change according to places
Weight
a) Unit isN
b) Measured by using spring balance
f) Its measurement is mg
g) Its value is O at the centre of the earth

Question 6.
For a body of mass 70 kg,
a) What is the weight of the body, if it is at the centre of the earth?
b) What is its mass on the Jupiter?
Answer:
a) Zero
b) 70 kg (Mass of a body will not change according to the change of place).

Question 7.
Correct the statement if wrong.
An object moving with uniform speed along a circular path undergoes velocity change due to the change in speed.
Answer:
An object moving with a uniform speed along a circular path undergoes velocity change due to change in direction.

Question 8.
Amal is on a merry-go-round in an amusement park.
a) What type of motion is he experiencing?
b) Which force helps him keep moving in circular path and what is its direction?
Answer:
a) Circular motion
b) Centripetal force.
It is directed towards the centre of the merry-go-round.

Question 9.
Acceleration due to gravity is independent of……………….
(mass of the object / mass of the Earth /radius of the Earth)
Answer:
mass of the object

Question 10.
Observe the figure

What change may happen to the force when the value of m₁, m₂ and d are doubled?
a) Doubled
b) Halved
C) No change
d) Reduced to 1/4
Answer:
e) No change

Question 11.
The gravitational force of attraction between two bodies of masses m₁ and m₂ separated by a distance ‘d’ is, F = \(\frac{G m_1 m_2}{d^2}\).The value of ‘G’ is
Answer:
c) 6.67 × 10^-11 Nm²/kg²

Question 12.
Observe the figures related to the feather and coin experiment conducted by Isaac Newton. Which is the evacuated tube in the given figures?

Answer:
figure 2

Question 13.
If the distance between two bodies that attract each other is doubled, how many times more will be their mutual force of attraction?
Answer:
1/4 times

Question 14.
Will the value of g be the same everywhere on the earth?
Answer:
No

Question 15.
Value of ‘g’ at the centre of the earth is _____
Answer:
Zero

Question 16.
What is force of gravity?
Answer:
Earth attracts all objects. The direction o this force is towards the centre of the Earth. This force of attraction is the force of gravity.

Question 17.
An object weighs 40 kg wt. on the earth. What ¡s its weight on the moon?
Answer:
Weight in moon = \(\frac{40}{9.8}\) × 1.62 = 6.6 kgwt

Question 18.
The value of ‘g’ on earth and moon are different. Compare the weight of a body having a mass of 100 kg on the surface of earth and moon (Value of g on earth 9.8 m/s² value of g on moon 1.62 m/s²).
Answer:
100 kg
Weight on Earth = mg = 100 × 9.8 = 980 N
Weight on Moon = mg = 100 × 1.62 = 162 N

Question 19.
A body of mass 10000 kg and another body of mass 4000 kg are separated by a distance of 2 m. What is the force of attraction
between them?
Answer:
m₁ = 10000 kg
m₂ = 4000 kg
d = 2m
G = 6.67 × 10 -11 Nm²/kg²

F = \(\frac{G m_1 m_2}{d^2}\) = \(\frac{6.67 \times 10^{-11} \times 10000 \times 4000}{2^2}\) = 6.67 × 10^-4 N

Question 20.
Two metal spheres of mass 100 g and 200 g are allowed to fall down simultaneously from the same height.
a) Which one will reach the ground first?
b) Justify your answer.
Answer:
a) Both of them reach the ground simultaneously.
b) Because the acceleration due to gravity does not depend on the mass of the object. Hence, both of them have equal acceleration.

Question 21.
The weight of an object is 60 N on earth. But its weight on the moon is approximately 10 N.
a) Write the factors on which the weight of an object depends.
b) The object experiences less weight on the moon. Why?
Answer:
a) Mass of the object, acceleration due to gravity.
b) Weight of an object, W = mg. In the moon, the value of ‘g’ is low. Hence, the object experiences less weight.

Question 22.
If a stone of mass 10kg and another of mass 5 kg fall down simultaneously from the top of a building, which one will reach the ground first? Why?
Answer:
They will reach at the same time.
(Acceleration due to gravity does not depend on the mass of the body.)

Question 23.
State true or false.
a) The value of G Is constant everywhere in the universe.
b) The value of g is constant everywhere in the universe.
c) The weight of an object ¡s constant everywhere ¡n the universe.
Answer:
a) True
b) False
c) False

Question 24.
Observe the figure

Assume that a body of mass 1 kg is kept at three places of earth marked as A, B, C,
a) In which place this body experiences maximum weight?
b) In which place this body experiences minimum weight?
c) Justify your answer.
Answer:
a) A
b) Weight at B will be less than that at A.Weight at C Will be Zero.
c) Weight= m × g but g = GM/R² Here, R is the radius of the earth. As R decreases, weight increases and as R increases, weight
decreases. The radius of the Earth (R) is not the same everywhere because the Earth is not a perfect sphere.

Question 25.
Observe the figures.

a) In which figure the attractive force is greater?
b) Calculate the attractive force in figure B
Answer:
a) A
b) m₁ = 5kg
m₂ = 20 kg
d = 10 m
F = \(\frac{G m_1 m_2}{d^2}\) = \(\frac{6.67 \times 10^{-11} \times 5 \times 20}{10^2}\)
= 6.67 × 10¹¹ N

Question 26.
Two objects of masses 40 kg and 20 kg are placed at different distances is depicted.

a) The distance between the objects in figure (2) is half of that in figure (1). The gravitational force of attraction in figure(2) is________ times that in figure (1)
b) State Newton’s Universal Law of Gravitation.
c) Calculate the Gravitational force of attraction in figure (1). (The value of G need not be substituted.)
Answer:
a) 4 times
b) The law states that all bodies in the universe attract each other. The force of attraction between two bodies is directly proportional to the product of their masses and inversely proportional to the square of the distance between them.
c) F = \(\frac{G m_1 m_2}{d^2}\) = \(\frac{G \times 20 \times 40}{4^2}\) = 50G N

Question 27.
Observe the instruments A,B shown in the figure.

Among these which is used to measure weight? (Instrument A, Instrument B)
Answer:
Instrument B

Question 28.
What is the relation between centripetal force and centripetal acceleration?
Answer:
The force required to produce centripetal acceleration is centripetal force.

Question 29.
A spring balance with a body suspended from it is allowed to fall.
a) What will be the reading on the balance during the fall?
b) What do you mean by free fall?
Answer:
a) 0
b) When a body is allowed to fall from a certain height, it falls to the Earth due to the force of gravity. This is free fall.

Question 30.

a) Name the devices in the figure
b) Which among these devices is used to measure weight of a body?
c) What do you mean by one kilogram weight?
Answer:
a) (i) Common balance
(ii) Spring balance
b) Spring balance (ii)
c) 1 kilogram weight is the attractive force exerted by the earth on an object of mass 1 kg.

Question 31.
The weight of a body is different at different places on the earth’s surface.
a) Where on th earth’s surface, does a body experience maximum weight?
(pole region, equatorial region, centre of earth).
b) What is the unit of weight?
c) Which is the instrument used to measure the weight of a body?
Answer:
a) Pole region
b) N or kgwt
c) Spring Balance

Question 32.
The figure shows the motion of an object along a circular path.

a) What do you mean by uniform circular motion?
b) Write any one example for uniform circular motion.
c) If this object loses centripetal force at the point A while in circular motion, draw the path of its movement.
Answer:
a) If the object swept equal distance at equal intervals of time in a circular path it is unifom circular motion.
b) The earth revolves around the sun.

Question 33.
Mass and weight of a body is determined at the pole and at the equator
a) Is there any difference in the mass?
b) Is there any change ¡n the weight?
c) Justify the answer.
Answer:
a) No change in mass
b) Change will occur
c) Mass is the quantity of matter present in a body. The value of g is greater at the poles and lesser at the equator. So, weight varies. The value of g does not affect the mass.

Question 34.
The motion of different objects is given below. The motion of a stone dropped from a height.

• The motion of a ball thrown vertically upwards.
• A lift moving downwards.

a) Which motion represents free fall?
b) What will be the weight of an object when it is in free fall? Explain the reason.
Answer:
a) The motion of a stone dropped from a height.
b) The weight of an object is zero during free fall. When an object is in free fall the gravitational force of attraction is completely utilized to accelerate the object. Hence, the body experiences weightlessness, or the weight of the body will be zero.

Question 35.
a) The weight of a freely falling body is zero. Why?
b) What do you mean by free fall?
c) A coconut gets detached from a coconut tree and hits the ground in I second. Calculate its velocity just before hitting the ground.
Answer:
a) Weight of the body (Gravitational Force) is utilised to give acceleration to the body.
b) If an object falls under Gravitational Force alone. its falling is called free fall.
e) u = 0
a = g = 9.8 m/s²
t = 1s
v = u + at = 0 + 9.8 × 1 = 9.8 m/s

Question 36.
Mass of a body is 10 kg.
a) Find the weight of the body.
b) Find the mass of the body when it is placed at the centre of the earth.
C) Find the weight of the body if it is placed on the surface of ‘Jupiter’.
(Value of g at Jupiter g = 23.1 m/s²)
Answer:
a) m = 10 kg
Weight = m × g = 10 × 9.8 = 98 N
b) mass = 10 kg
c) Weight at surface of Jupiter = m × g = 10 × 23.1 = 231 N

Question 37.
A body of mass 10 kg is taken to different parts of the earth.
a) What is its mass at the centre of the earth?
b) Where does it have maximum weight?
c) At which part on the surface of the earth the weight is minimum?
d) In your opinion what is the cause of this difference in eight?
Answer:
a) 10kg
b) At poles
c) At equatorial places
d) As the radius of the earth (R) changes, the value of g \(\left(g=\frac{G M}{R^2}\right)\) changes, and weight (w = mg) changes.

Question 38.
The motion of an object along a circular path is known as circular motion.
a) What is meant by centripetal acceleration?
b) A hammer of mass 4 kg is subjected to circular motion along a circular path of radius 2 m with a velocity of 5 m/s. Calculate its centripetal force.
c) What happens to the hammer which is tinder circular motion ¡fit loses the centripetal force.
Answer:
a) The acceleration experienced by an object in a circular motion, along the radius, towards the centre of the circle, is known as centripetal
acceleration. The force that creates a centripetal acceleration is called centripetal force. Centripetal acceleration and centripetal force are directed towards the centre.

b) m = 4kg; v = 5m/s; r = 2m
F_c = \(\frac{m v^2}{r}\) = \(\frac{4 \times 5^2}{2}\) = 50 N

c) [t will be thrown off along the tangent at that point.

Question 39.
Observe the figure. A, B, C are three positions on the surface of the earth and D is the centre of the earth.

a) Is the value of mass or weight of an object is same at all positions on the surface of the earth.
b) What is the weight of an object at D?
c) On the surface of the. earth at which positions among A, B and C the value of acceleration due to gravity be maximum. Justify your answer.
Answer:
a) Mass of an object is same at all positions on the surface of the earth but weight of the object varies.
b) Zero
e) Value of acceleration due to gravity is maximum at A. Acceleration due to gravity, ‘g’ depends on the radius of the earth. As the radius decreases ‘g increases. The distance to A(Pole) is less than that of other positions.