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Lakhmir Singh solutions for Class 9 Science chapter 3 - Gravitation

Science for Class 9 Part 1 Physics

Lakhmir Singh Science Class 9 Part 1 Physics Chapter 3: Gravitation

Chapter 3: Gravitation Exercise Very Short Answers, Short Answers, Long Answers, MCQ, Hots Questions solutions [Pages 100 - 104]

Very Short Answers | Q 1 | Page 100

What is the value of gravitational constant G (i) on the earth, and (ii) on the moon ?

Very Short Answers | Q 2 | Page 100

Which force is responsible for the moon revolving round the earth ?

Very Short Answers | Q 3 | Page 100

Does the acceleration produced in a freely falling body depend on the mass of the body ?

Very Short Answers | Q 4 | Page 100

Name the scientist who gave the three laws of planetary motion.

Very Short Answers | Q 5 | Page 100

Name the scientist who explained the motion of planets on the basis of gravitational force between the sun and planets.

Very Short Answers | Q 6 | Page 100

State the Kepler’s law which is represented by the relation r3 ∝ T2.

Very Short Answers | Q 7 | Page 100

Which of the Kepler’s laws of planetary motion led Newton to establish the inverse-square rule for gravitational force between two bodies ?

Very Short Answers | Q 8 | Page 100

Name the property of earth which is responsible for extremely small acceleration being produced in it as a result of attraction by other small objects.

Very Short Answers | Q 9 | Page 100

What is the acceleration produced in a freely falling body of mass 10 kg ? (Neglect air resistance)

Very Short Answers | Q 10 | Page 100

When an object is dropped from a height, it accelerates and falls down. Name the force which accelerates the object.

Very Short Answers | Q 11 | Page 100

Give the formula for the gravitational force F between two bodies of masses M and m kept at a distance d from each other.

Very Short Answers | Q 12 | Page 100

What force is responsible for the earth revolving round the sun ?

Very Short Answers | Q 13 | Page 100

What name has been given to the force with which two objects lying apart attract each other ?

Very Short Answers | Q 14 | Page 100

What type of force is involved in the formation of tides in the sea ?

Very Short Answers | Q 15 | Page 100

Which force is responsible for holding the solar system together ?

Very Short Answers | Q 16 | Page 100

What is the weight of a 1 kilogram mass on the earth ? (g = 9.8 m/s2).

Very Short Answers | Q 17 | Page 100

On what factor/factors does the weight of a body depend ?

Very Short Answers | Q 18 | Page 100

As the altitude of a body increases, do the weight and mass both vary ?

Very Short Answers | Q 19 | Page 100

If the same body is taken to places having different gravitational field strength, then what will vary: its weight or mass ?

Very Short Answers | Q 20 | Page 100

If the mass of an object be 10 kg, what is its weight ? (g = 9.8 m/s2).

Very Short Answers | Q 21 | Page 100

The weight of a body is 50 N. What is its mass ? (g = 9.8 m/s2).

Very Short Answers | Q 22 | Page 100

A body has a weight of 10 kg on the surface of earth. What will be its weight when taken to the centre of the earth ?

Very Short Answers | Q 23 | Page 100

Write down the weight of a 50 kg mass on the earth, (g = 9.8 m/s2).

Very Short Answers | Q 24 | Page 100

If the weight of a body on the earth is 6 N, what will it be on the moon ?

Very Short Answers | Q 25.1 | Page 100

State whether the following statement is true or false :
A falling stone also attracts the earth.

Very Short Answers | Q 25.2 | Page 100

State whether the following statement is true or false :

The force of gravitation between two objects depends on the nature of medium between them.

Very Short Answers | Q 25.3 | Page 100

State whether the following statement is true or false :

The value of G on the moon is about one-sixth (1/6)of the value of G on the earth.

Very Short Answers | Q 25.4 | Page 100

State whether the following statement is true or false :

The acceleration due to gravity acting on a freely falling body is directly proportional to the mass of the body.

Very Short Answers | Q 25.5 | Page 100

State whether the following statement is true or false :

The weight of an object on the earth is about one-sixth of its weight on the moon.

Very Short Answers | Q 26.1 | Page 101

Fill in the following blank with suitable word :

The acceleration due to gravity on the moon is about ………………of that on the earth.

Very Short Answers | Q 26.2 | Page 101

Fill in the following blank with suitable word :

In order that the force of gravitation between two bodies may become noticeable and cause motion, one  of the bodies must have an extremely large……………………………..

Very Short Answers | Q 26.3 | Page 101

Fill in the following blank with suitable word :

The weight of an object on the earth is about……………….. of its weight on the moon.

Very Short Answers | Q 26.4 | Page 101

Fill in the following blank with suitable word :

The weight of an object on the moon is about …………………….. of its weight on the earth.

Very Short Answers | Q 26.5 | Page 101

Fill in the following blank with suitable word :

The value of g on the earth is about………………. of that on the moon.

Very Short Answers | Q 26.6 | Page 101

Fill in the following blank with suitable word :

If the weight of a body is 6 N on the moon, it will be about……………………… on the earth.

Short Answers | Q 27 | Page 101

Explain what is meant by the equation :
g= Gxxm/r^2
where the symbols have their usual meanings.

Short Answers | Q 28.1 | Page 101

What do you mean by the term free fall ?

Short Answers | Q 28.2 | Page 101

During a free fall, will heavier objects accelerate more than lighter ones ?

Short Answers | Q 29 | Page 101

Can we apply Newton’s third law to the gravitational force ? Explain your answer.

Short Answers | Q 30 | Page 101

Give reason for the following :
The force of gravitation between two cricket balls is extremely small but that between a cricket ball and the earth is extremely large.

Short Answers | Q 31 | Page 101

Describe how the gravitational force between two objects depends on the distance between them.

Short Answers | Q 32 | Page 101

What happens to the gravitational force between two objects when the distance between them is :
(1) doubled ?
(2) halved ?

Short Answers | Q 33 | Page 101

State two applications of universal law of gravitation.

Short Answers | Q 34 | Page 101

Explain why, if a stone held in our hand is released, it falls towards the earth.

Short Answers | Q 35 | Page 101

Calculate the force of gravitation between two objects of masses 50 kg and 120 kg respectively kept at a distance of 10 m from one another. (Gravitational constant, G = 6.7 x 10-11 Nm2 kg-2)

Short Answers | Q 36 | Page 101

What is the force of gravity on a body of mass 150 kg lying on the surface of the earth? (Mass of earth = 6 x 1024 kg; Radius of earth = 6.4 x 106 m; G = 6.7 x 10-11 Nm2/kg2)

Short Answers | Q 37 | Page 101

The mass of sun is 2 ✕ 1030 kg and the mass of earth is 6 ✕ 1024 kg. If the average distance between the sun and the earth be 1.5 ✕ 108 km, calculate the force of gravitation between them.

Short Answers | Q 38 | Page 101

A piece of stone is thrown vertically upwards. It reaches the maximum height in 3 seconds. If the acceleration of the stone be 9.8 m/s2 directed towards the ground, calculate the initial velocity of the stone with which it is thrown upwards

Short Answers | Q 39 | Page 101

A stone falls from a building and reaches the ground 2.5 seconds later. How high is the building ? (g =9.8 m/s2)

Short Answers | Q 40 | Page 101

A stone is dropped from a height of 20 m.

(i) How long will it take to reach the ground?
(ii) What will be its speed when it hits the ground? (g = 10 m/s2)

Short Answers | Q 41 | Page 101

A stone is thrown vertically upwards with a speed of 20 m/s. How high will it go before it begins to fall ? (g =9.8 m/s2)

Short Answers | Q 42 | Page 101

When a cricket ball is thrown vertically upwards, it reaches a maximum height of 5 metres.
(a) What was the initial speed of the ball ?
(b) How much time is taken by the ball to reach the highest point ? (g=10 ms-2)

Short Answers | Q 43 | Page 101

Write the differences between mass and weight of an object.

Short Answers | Q 44 | Page 101

Can a body have mass but no weight ? Give reasons for your answer.

Short Answers | Q 45 | Page 102

A force of 20 N acts upon a body whose weight is 9.8 N. What is the mass of the body and how much is its acceleration ? (g = 9.8 m s-2).

Short Answers | Q 46 | Page 102

A stone resting on the ground has a gravitational force of 20 N acting on it. What is the weight of the stone ? What is its mass ? (g = 10 m/s2).

Short Answers | Q 47 | Page 102

An object has mass of 20 kg on earth. What will be its (1) mass, and (2) weight, on the moon ? (g on moon = 1.6 m/s2).

Short Answers | Q 48 | Page 102

Which is more fundamental, the mass of a body or its weight ? Why ?

Short Answers | Q 49 | Page 102

How much is the weight of an object on the moon as compared to its weight on the earth ? Give reason for your answer. Long Answers | Q 50.1 | Page 102

Define mass of a body. What is the SI unit of mass ?

Long Answers | Q 50.2 | Page 102

Define weight of a body. What is the SI unit of weight ?

Long Answers | Q 50.3 | Page 102

What is the relation between mass and weight of a body ?

Long Answers | Q 51.1 | Page 102

State the universal law of gravitation. Name the scientist who gave this law.

Long Answers | Q 51.2 | Page 102

Define gravitational constant. What are the units of gravitational constant ?

Long Answers | Q 52.1 | Page 102

What do you understand by the term 'acceleration due to gravity of earth' ?

Long Answers | Q 52.2 | Page 102

What is the usual value of the acceleration due to gravity of earth ?

Long Answers | Q 52.3 | Page 102

State the SI unit of acceleration due to gravity.

Long Answers | Q 53.1 | Page 102

Is the acceleration due to gravity of earth ‘g’ a constant ? Discuss.

Long Answers | Q 53.2 | Page 102

Calculate the acceleration due to gravity on the surface of a satellite having a mass of 7.4 x 1022 kg and a radius of 1.74 x 106 m (G = 6.7 x 10-11 Nm2/kg2). Which satellite do you think it could be ?

Long Answers | Q 54 | Page 102

State and explain Keplers laws of planetary motion. Draw diagrams to illustrate these laws.

Long Answers | Q 55 | Page 102

The mass of a planet is 6 x 1024 kg and its diameter is 12.8 x 103 If the value of gravitational constant be 6.7 x 10-11 Nm2/kg2, calculate the value of acceleration due to gravity on the surface of the planet. What planet could this be

MCQ | Q 56 | Page 102

An object is thrown vertically upwards with a velocity u, the greatest height h to which it will rise before falling back is given by :

• u/g

• u2/2g

• u2/g

• u/2g

MCQ | Q 57 | Page 102

The mass of moon is about 0.012 times that of earth and its diameter is about 0.25 times that of earth. The value of G on the moon will be:

• less than that on the earth

• more than that on the earth

• same as that on the earth

• about one-sixth of that on the earth

MCQ | Q 58 | Page 102

The value of g on the surface of the moon :

• is the same as on the earth

• is less than that on the earth

• is more than that on the earth

• keeps changing day by day

MCQ | Q 59 | Page 102

The atmosphere consisting of a large number of gases is held to the earth by :

• winds

• clouds

• earth's magnetic field

• gravity

MCQ | Q 60 | Page 102

The force of attraction between two unit point masses separated by a unit distance is called :

• gravitational potential

• acceleration due to gravity

• gravitational field strength

•  universal gravitational constant

MCQ | Q 61 | Page 103

The weight of an object at the centre of the earth of radius R is :

• Zero

• R times the weight at the surface of the earth

• Infinite

• 1/R2 times the weight at the surface of the earth

MCQ | Q 62 | Page 103

Two objects of different masses falling freely near the surface of moon would :

• have same velocities at any instant

• have different accelerations

• experience forces of same magnitude

• undergo a change in their inertia

MCQ | Q 63 | Page 103

The value of acceleration due to gravity of earth :

• is the same on equator and poles

•  is the least on poles

• is the least in equator

• increases from pole to equator

MCQ | Q 64 | Page 103

The law of gravitation gives the gravitational force between :

•  the earth and a point mass only

• the earth and the sun only

• any two bodies having some mass

• any two charged bodies only

MCQ | Q 65 | Page 103

The value of quantity G in the formula for gravitational force :

• depends on mass of the earth only

• depends on the radius of earth only

• depends on both mass and radius of earth

• depends neither on mass nor on radius of earth

MCQ | Q 66 | Page 103

Two particles are placed at some distance from each other. If, keeping the distance between them unchanged, the mass of each of the two particles is doubled, the value of gravitational force between them will become :

• 1/4 times

•  1/2 times

• 4 times

• 2 times

MCQ | Q 67 | Page 103

In the relation F = G ✕ M ✕ m/d2, the quantity G:

• depends on the value of g at the place of observation

• is used only when the earth is one of the two masses

• is the greatest on the surface of the earth

•  is of the same value irrespective of the place of observation

MCQ | Q 68 | Page 103

The gravitational force of attraction between two objects is x. Keeping the masses of the objects unchanged, if the distance between the objects is halved, then the magnitude of gravitational force between them will become :

• x/4

• x/2

• 2x

• 4x

MCQ | Q 69 | Page 103

An apple of mass 100 g falls from a tree because of gravitational attraction between the earth and the apple. If the magnitude of force exerted by the earth on the apple be F1 and the magnitude for force exerted by the apple on the earth be F2, then :

• F1 is very much greater than F2

• F2 is very much greater than F1

• F1 is only a little grater than F2

• F1 and F2 are exactly equal

MCQ | Q 70 | Page 103

According to one of the Kepler's laws of planetary motion :

• r2 ∝ T3

• r ∝ T2

• r3 ∝ T2

• r^3 ∝ 1/T^2

Hots Questions | Q 71 | Page 103

If the distance between two masses is increased by a factor of 5, by what factor would the mass of one of them have to be altered to maintain the same gravitational force ? Would this be an increase or decrease in the mass ?

Hots Questions | Q 72 | Page 103

Universal law of gravitation states that every object exerts a gravitational force of attraction on every other object. If this is true, why don’t we notice such forces ? Why don’t the two objects in a room move towards each other due to this force ?

Hots Questions | Q 73 | Page 103

Suppose a planet exists whose mass and radius both are half those of the earth. Calculate the acceleration due to gravity on the surface of this planet.

Hots Questions | Q 74 | Page 104

A coin and a piece of paper are dropped simultaneously from the same height. Which of the two will touch the ground first ? What will happen if the coin and the piece of paper are dropped in vacuum ? Give reasons for your answer.

Hots Questions | Q 75 | Page 104

A stone and the earth attract each other with an equal and opposite force. Why then we see only the stone falling towards the earth but not the earth rising towards the stone ?

Hots Questions | Q 76 | Page 104

What is the actual shape of the orbit of a planet around the sun? What assumption was made by Newton regarding the shape of an orbit of a planet around the sun of deriving his inverse square rule from Kepler's third law of planetary motion?

Hots Questions | Q 77 | Page 104

The values of g at six distances A, B, C, D, E and F from the surface of the earth are found to be 3.08 m/s2, 9.23 m/s2, 0.57 m/s2, 7.34 m/s2, 0.30 m/s2 and 1.49 m/s2, respectively.
(a) Arrange these values of g according to the increasing distances from the surface of the earth (keeping the value of g nearest to the surface of the earth first)
(b) If the value of distance F be 10000 km from the surface of the earth, state whether this distance is deep . inside the earth or high up in the sky. Give reason for your answer.

Chapter 3: Gravitation Exercise Very Short Answers, Short Answers, Long Answers, MCQ, Hots Questions solutions [Pages 123 - 128]

Very Short Answers | Q 1 | Page 123

Write the common unit of density.

Very Short Answers | Q 2 | Page 123

What is the density of water in SI units ?

Very Short Answers | Q 3 | Page 123

What is the value of relative density of water ?

Very Short Answers | Q 4 | Page 123

Name the quantity whose one of the units is pascal (Pa).

Very Short Answers | Q 5 | Page 123

State the units in which pressure is measured.

Very Short Answers | Q 6.1 | Page 123

State whether the following statement is true or false :

The buoyant force depends on the nature of object immersed in the liquid

Very Short Answers | Q 6.2 | Page 123

State whether the following statement is true or false :

Archimedes’ principle can also be applied to gases.

Very Short Answers | Q 7 | Page 123

In which direction does the buoyant force on an object due to a liquid act ?

Very Short Answers | Q 8 | Page 123

What is the other name of buoyant force ?

Very Short Answers | Q 9 | Page 123

Name the force which makes heavy objects appear light when immersed in a liquid.

Very Short Answers | Q 10 | Page 123

What is upthrust  ?

Very Short Answers | Q 11 | Page 123

Name the principle which gives the magnitude of buoyant force acting on an object immersed in a liquid.

Very Short Answers | Q 12 | Page 123

The relative density of mercury is 13.6. What does this statement mean?

Very Short Answers | Q 13 | Page 123

What name is given to thrust per unit area ?

Very Short Answers | Q 14 | Page 123

What is the scientific name of the 'upward force' acting on an object immersed in a liquid?

Very Short Answers | Q 15 | Page 123

What is meant by the term ‘buoyancy’ ?

Very Short Answers | Q 16 | Page 123

What causes buoyant force (or upthrust) on a boat ?

Very Short Answers | Q 17 | Page 123

Why does ice float in water ?

Very Short Answers | Q 18 | Page 123

What force acting on an area of 0.5 m2 will produce a pressure of 500 Pa ?

Very Short Answers | Q 19 | Page 123

An object of weight 200 N is floating in a liquid. What is the magnitude of buoyant force acting on it ?

Very Short Answers | Q 20 | Page 123

Name the scientist who gave he magnitude of buoyant force acting on a solid object immersed in a liquid.

Very Short Answers | Q 21 | Page 123

The density of gold is 19 g/cm3. Find the volume of 95 g of gold.

Very Short Answers | Q 22 | Page 123

What is the mass of 5 m3 of cement of density 3000 kg/m3 ?

Very Short Answers | Q 23 | Page 123

What is the density of a substance of mass 100 g and volume 10 cm3 ?

Very Short Answers | Q 24 | Page 123

Why does a block of wood held under water rise to the surface when released ?

Very Short Answers | Q 25 | Page 123

The density of a body is 800 kg/m3. Will it sink or float when dipped in a bucket of water ? (Density of water = 1000 kg/m3).

Very Short Answers | Q 26.1 | Page 123

Fill in the blank with suitable word :
Force acting on a unit area is called...................

Very Short Answers | Q 26.2 | Page 123

Fill in the blank with suitable word :
It is the................. force which makes objects appear lighter in water.

Very Short Answers | Q 26.3 | Page 123

Fill in the blank with suitable word :
A heavy ship floats in water because its....................density is less than that of water.

Very Short Answers | Q 26.4 | Page 123

Fill in the blank with suitable word :

In fluids (liquids and gases), pressure acts in....................directions, and pressure.................as the depth increases.

Very Short Answers | Q 26.5 | Page 123

Fill in the blank with suitable word :

In order to sink in a fluid, the density of an object must be .................. than the ................ of the fluid.

Very Short Answers | Q 26.6 | Page 123

Fill in the blank with suitable word :

Snow shoes work by spreading out a person’s .................... over a much bigger .................. .

Very Short Answers | Q 26.7 | Page 123

Fill in the blank with suitable word :

If the area of a snow shoe is five times....................... than the area of an ordinary shoe, then the pressure of a snow shoe on the snow is five times...............

Short Answers | Q 27.1 | Page 124

What is the difference between the density and relative density of a substance ?

Short Answers | Q 27.2 | Page 124

If the relative density of a substance is 7.1, what will be its density in SI units ?

Short Answers | Q 28 | Page 124

Define thrust. What is its unit ?

Short Answers | Q 29 | Page 124

A mug full of water appears light as long as it is under water in the bucket than when it is outside water. Why ?

Short Answers | Q 30 | Page 124

What happens to the buoyant force as more and more volume of a solid object is immersed in a liquid ? When does the buoyant force become maximum ?

Short Answers | Q 31 | Page 124

Why do we feel light on our feet when standing in a swimming pool with water up to our armpits ?

Short Answers | Q 32 | Page 124

Explain why, big boulders can be moved easily by flood.

Short Answers | Q 33 | Page 124

An iron nail sinks in water but it floats in mercury. Why ?

Short Answers | Q 34 | Page 124

Explain why, a piece of glass sinks in water but it floats in mercury.

Short Answers | Q 35 | Page 124

Steel sinks in water but a steel boat floats. Why ?

Short Answers | Q 36 | Page 124

Explain why, school bags are provided with wide straps to carry them.

Short Answers | Q 37 | Page 124

Why does a sharp knife cut objects more effectively than a blunt knife ?

Short Answers | Q 38 | Page 124

Explain why, wooden (or concrete) sleepers are kept below the railway line.

Short Answers | Q 39 | Page 124

Explain why, a wide steel belt is provided over the wheels of an army tank. Short Answers | Q 40 | Page 124

Explain why, the tip of a sewing needle is sharp. Short Answers | Q 41 | Page 124

When is the pressure on the ground more—when a man is walking or when a man is standing ? Explain.

Short Answers | Q 42 | Page 124

Explain why, snow shoes stop you from sinking into soft snow.

Short Answers | Q 43 | Page 124

Explain why, when a person stands on a cushion, the depression is much more than when he lies down on it.

Short Answers | Q 44 | Page 124

Use your ideas about pressure to explain why it is easier to walk on soft sand if you have flat shoes rather than shoes with sharp heels.

Short Answers | Q 45 | Page 124

Explain why, a nail has a pointed tip. Short Answers | Q 46 | Page 125

Explain why, buildings and dams have wide foundations.

Short Answers | Q 47 | Page 125

Why does a ship made of iron and steel float in water whereas a small piece of iron sinks in it ?

Short Answers | Q 48 | Page 125

Why do camels have large flat feet ? Short Answers | Q 49.1 | Page 125

Name the force the upward push of water on a submerged object .

Short Answers | Q 49.2 | Page 125

Name the force which wears away two surfaces as they move over one another.

Short Answers | Q 49.3 | Page 125

Name the force which pulled the apple off Isaac Newton’s tree.

Short Answers | Q 49.4 | Page 125

Name the force which stops you falling through the floor.

Short Answers | Q 50 | Page 125

A pressure of 10 Pa acts on an area of 3.0 m2. What is the force acting on the area ? What force will be exerted by the application of same pressure if the area is made one-third ?

Short Answers | Q 51.1 | Page 125

A girl is wearing a pair of flat shoes. She weighs 550 N. The area of contact of one shoe with the ground is 160 cm2. What pressure will be exerted by the girl on the ground if she stands on two feet ?

Short Answers | Q 51.2 | Page 125

A girl is wearing a pair of flat shoes. She weighs 550 N. The area of contact of one shoe with the ground is 160 cm2. What pressure will be exerted by the girl on the ground if she stands on one foot ?

Short Answers | Q 52 | Page 125

Calculate the density of an object of volume 3 m3 and mass 9 kg. State whether this object will float or sink in water. Give reason for your answer.

Short Answers | Q 53 | Page 125

An object weighs 500 grams in air. This object is then fully immersed in water. State whether it will weigh less in water or more in water. Give reason for your answer.

Short Answers | Q 54.1 | Page 125

Write down an equation that defines density.

Short Answers | Q 54.2 | Page 125

5 kg of material A occupy 20 cm3 whereas 20 kg of materia! B occupy 90 cm3. Which has the greater density : A or B ? Support your answer with calculations.

Long Answers | Q 55.1 | Page 125

Define buoyant force. Name two factors on which buoyant force depends.

Long Answers | Q 55.2 | Page 125

What is the cause of buoyant force ?

Long Answers | Q 55.3 | Page 125

When a boat is partially immersed in water, it displaces 600 kg of water. How much is the buoyant force acting on the boat in newtons ? (g = 10 m s-2)

Long Answers | Q 56.1 | Page 125

State the principle of flotation.

Long Answers | Q 56.2 | Page 125

A floating boat displaces water weighing 6000 newton.
What is the weight of the boat ?

Long Answers | Q 56.2 | Page 125

A floating boat displaces water weighing 6000 newton.

What is the buoyant force on the boat ?

Long Answers | Q 57.1 | Page 125

Define density. What is the SI unit of density ?

Long Answers | Q 57.2 | Page 125

Define relative density. What is the SI unit of relative density ?

Long Answers | Q 57.3 | Page 125

The density of turpentine is 840 kg/m3. What will be its relative density ? (Density of water = 1000 kg/m3)

Long Answers | Q 58.1 | Page 125

Define pressure.

Long Answers | Q 58.2 | Page 125

What is the relation between pressure, force and area ?

Long Answers | Q 58.3 | Page 125

Calculate the pressure when a force of 200 N is exerted on an area of 5 m2 .

Long Answers | Q 58.3 | Page 125

Calculate the pressure when a force of 200 N is exerted on an area of 10 m2

Long Answers | Q 59.1 | Page 126

What are fluids ?  Name two common fluids.

Long Answers | Q 59.2 | Page 126

State Archimedes principle.

Long Answers | Q 59.3 | Page 126

When does an object float or sink when placed on the surface of a liquid ?

Long Answers | Q 60.1 | Page 126

How does a boat float in water ?

Long Answers | Q 60.2 | Page 126

A piece of steel has a volume of 12 cm3, and a mass of 96 g. What is its density in g/cm3 ?

Long Answers | Q 60.2 | Page 126

A piece of steel has a volume of 12 cm3, and a mass of 96 g. What is its density in kg/m3 ?

Long Answers | Q 61.1 | Page 126

An elephant weighing 40,000 N stands on one foot of area 1000 cm2 whereas a girl weighing 400 N is standing on one ‘stiletto’ heel of area 1 cm2.
Which of the two, elephant or girl, exerts a larger force on the ground and by how much? Long Answers | Q 61.2 | Page 126

An elephant weighing 40,000 N stands on one foot of area 1000 cm2 whereas a girl weighing 400 N is standing on one 'stiletto' heel of area 1 cm2.
What pressure is exerted on the ground by the elephant standing on one foot? Long Answers | Q 61.3 | Page 126

An elephant weighing 40,000 N stands on one foot of area 1000 cm2 whereas a girl weighing 400 N is standing on one ‘stiletto’ heel of area 1 cm2.
What pressure is exerted on the ground by the girl standing on one heel ? Long Answers | Q 61.4 | Page 126

An elephant weighing 40,000 N stands on one foot of area 1000 cm2 whereas a girl weighing 400 N is standing on one ‘stiletto’ heel of area 1 cm2.
Which of the two exerts larger pressure on the ground : elephant or girl? Long Answers | Q 61.5 | Page 126

An elephant weighing 40,000 N stands on one foot of area 1000 cm2 whereas a girl weighing 400 N is standing on one ‘stiletto’ heel of area 1 cm2.
What is the ratio of pressure exerted by the girl to the pressure exerted by the elephant? MCQ | Q 62 | Page 126

An object weighs 10 N in air. When immersed fully in a liquid, it weighs only 8 N. The weight of liquid displaced by the object will be :

• 2 N

• 8 N

• 10 N

• 12 N

MCQ | Q 63 | Page 126

A rectangle wooden block has length, breadth and height of 50 cm, 25 cm and 10 cm, respectively. This wooden block is kept on ground in three different ways, turn by turn. Which of the following is the correct statement about the pressure exerted by this block on the ground?

• the maximum pressure is exerted when the length and breadth form the base

• the maximum pressure is exerted when length and height form the base

• the maximum pressure is exerted when breadth and height form the base

• the minimum pressure is exerted when length and height form the base

MCQ | Q 64 | Page 126

An object is put in three liquids having different densities, one by one. The object floats with 1/9 , 2/11 and 3/7 parts of its volume outside the surface of liquids of densities d1, d2 and d3 respectively. Which of the following is the correct order of the densities of the three liquids?

• d1 > d2 > d3

• d2 > d3 > d1

• d1 < d2 < d3

• d3 > d2 > d1

MCQ | Q 65 | Page 126

A metal in which even iron can float is :

• sodium

• magnesium

• mercury

• manganese

MCQ | Q 66 | Page 126

Four balls, A, B, C and D displace 10 mL, 24 mL, 15 mL and 12 mL of a liquid respectively, when immersed completely. The ball which will undergo the maximum apparent loss in weight will be :

• A

• B

• C

• D

MCQ | Q 67 | Page 126

The relative densities of four liquids P, Q, R and S are 1.26, 1.0, 0.84 and 13.6 respectively. An object is floated in all these liquids, one by one. In which liquid the object will float with its maximum volume submerged under the liquid?

• P

• Q

• R

• S

MCQ | Q 68 | Page 127

A solid of density 900 kg/m3 floats in oil as shown in the given diagram. The oil floats on water of density 1000 kg/m3 as shown. The density of oil kg/m3 could be : • 850

• 900

• 950

• 1050

MCQ | Q 69 | Page 127

The density of water is 1000 kg/m3 and the density of copper is 8900 kg/m3. Which of the following statements is incorrect?

• "The density of a certain volume of copper"/"The density of the same volume of water" = 8.9

• "The volume of a certain mass of copper"/"The volume of the same mass of water" = 8.9

• "The weight of a certain volume of copper"/"The weight of the same volume of water" = 8.9

• "The mass of a certain volume of copper"/"The mass of the same volume of water" = 8.9

MCQ | Q 70 | Page 127

The diagrams represent four measuring cylinders containing liquids. The mass and volume of the liquid in each cylinder are stated. Which two measuring cylinder could contain an identical liquid? • W and X

• W and Y

• X and Y

• X and Z

MCQ | Q 71 | Page 127

Consider the following information in respect of four objects A, B, C and D :

 Object Density(kg/m3) Volume(m3) Mass(kg) A 2 4000 B 8000 4 C 2000 1000 D 4 2000

Which object would float on water ?

• A

• B

• C

• D

Hots Questions | Q 72 | Page 127

If two equal weights of unequal volumes are balanced in air, what will happen when they are completely dipped in water ? Why ?

Hots Questions | Q 73 | Page 127

Two different bodies are completely immersed in water and undergo the same loss in weight. Is it necessary that their weights in air should also be the same ? Explain.

Hots Questions | Q 74 | Page 127

A body floats in kerosene of density 0.8 x 103 kg/m3 up to a certain mark. If the same body is placed in water of density 1.0 x 103 kg/m3, will it sink more or less ? Give reason for your answer.

Hots Questions | Q 75 | Page 127

Giving reasons state the reading on a spring balance when it is attached to a floating block of wood which weighs 50 g in air.

Hots Questions | Q 76 | Page 127

If a fresh egg is put into a beaker filled with water, it sinks. On dissolving a lot of salt in the water, the egg begins to rise and then floats. Why ?

Hots Questions | Q 77.1 | Page 128

A beaker full of water is suspended from a spring balance. Will the reading of the balance change if a cork is placed in water ?

Hots Questions | Q 77.2 | Page 128

A beaker full of water is suspended from a spring balance. Will the reading of the balance change if a piece of heavy metal is placed in it ?

Hots Questions | Q 78 | Page 128

When a golf ball is lowered into a measuring cylinder containing water, the water level rises by 30 cm3 when the ball is completely submerged. If the mass of ball in air is 33 g, find its density.

Hots Questions | Q 79.1 | Page 128

A boy get into a floating boat .

What happens to the boat ?

Hots Questions | Q 79.2 | Page 128

A boy get into a floating boat.

What happens to the weight of water displaced ?

Hots Questions | Q 79.3 | Page 128

A boy get into a floating boat.

What happens to the buoyant force on the boat ?

Hots Questions | Q 80 | Page 128

A 1/2 kg sheet of tin sinks in water but if the same sheet is converted into a box or boat, it floats. Why?

Chapter 3: Gravitation

Lakhmir Singh Science Class 9 Part 1 Physics Lakhmir Singh solutions for Class 9 Science chapter 3 - Gravitation

Lakhmir Singh solutions for Class 9 Science chapter 3 (Gravitation) include all questions with solution and detail explanation. This will clear students doubts about any question and improve application skills while preparing for board exams. The detailed, step-by-step solutions will help you understand the concepts better and clear your confusions, if any. Shaalaa.com has the CBSE Science for Class 9 Part 1 Physics solutions in a manner that help students grasp basic concepts better and faster.

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Concepts covered in Class 9 Science chapter 3 Gravitation are Universal Law of Gravitation, Relative Density, Archimedes' Principle, Thrust and Pressure - Why Objects Float Or Sink When Placed on the Surface of Water?, Thrust and Pressure - Pressure in Fluids, Thrust and Pressure - Buoyancy, Mass and Weight, Free Fall - Motion of Objects Under the Influence of Gravitational Force of the Earth, Free Fall - to Calculate the Value of g, Concept of Free Fall, Importance of the Universal Law of Gravitation, Gravitation.

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