Section A ( 2 x 7 = 14)1. The volume of a 50 gm sealed packet is 350 cm3. Will the packet float or sink in water if

the density of water is 1 g/cm3 ? What will be the mass of the water displaced by this packet  ?

2. In what direction does the buoyant force on an object, due to liquid act?3. Why does a buffalo float on the river but not the man?4. What do you mean by buoyancy?5. How do submarines float or sink as desired?6. You have a bag of cotton and an iron bar, each indicating a mass of 100 kg when

measured on a weighing machine. In reality, one is heavier than other. Can you say which one is heavier and why?

7. Why does a block of plastic released under water come up to the surface of water?

Section B (3 x 7 = 21)8. Why is it difficult to hold a school bag having a strap made of a thin and strong string?9. Why does an object float or sink when placed on the surface of water?10. Why the base of the dam made as wide as possible? 11. Ramesh buys 6 bottles of syrup each containing 1litre. Each empty bottle weighs 400g.

The density of syrup is 1.2 g/cm3. What weight does Ramesh have to carry home?12. The volume of 900g of a substance is 1000 cm3. Will the substance sink or float in water

if the density of water is 1g/cm3. What will be the mass of water displaced by the substance?

13. What is the up thrust experienced by a cube of edge – length 5cm made of iron when completely immersed in ethanol of density 0.8 g/cm3 

14. State Archimedes’ principle. Give any two applications of Archimedes principle?

Class XI Physics thrust Pressure and Buoyancy (Gravitation) NCERT Solutions

Thrust and Pressure, Pressure in Fluids, Buoyancy, Why objects

floats or sink when placed on the surface of water?,

Archimedes’ Principle, Relative Density

Why is it difficult to hold a school bag having a strap made of a

thin and strong string?

It is difficult to hold a school bag having a strap made of a thin and

strong string because it apply the large pressure on the shoulders due

to very small contact surface area . we know that the pressure is

inversely proportional to the surface area on which the force acts

What do you mean by buoyancy?

The tendency of a liquid to exert an upward force on an object

placed in it is called buoyancy. 

When a body is completely or partially immersed in a fluid, then the

upward thrust acting on the body is called force of buoyancy or

buoyant force.

It increases as we push the object deeper into water. The magnitude

of this buoyant force depends on the density of the fluid.

Why does an object float or sink when placed on the surface of

water?

An object floats or sinks when placed on the surface of water

because of the buoyant force acting on the object .

If the density of an object is less than the density of water it floats.

This means that the up thrust of water on an object is greater than the

weight of the object.

If the density of an object is more than the density of water it sinks.

This means that the up thrust of water on an object is less than the

weight of the object.

Therefore objects of density less than that of a liquid float on the

liquid. The objects of density greater than that of a liquid sink in the

liquid.

Why the cutting edge of a knife should be as sharp as possible? 

The cutting edge of a knife should as sharp to create greater pressure

even for a very small applied force for quick action.

You find your mass to be 42 kg on a weighing machine. Is your

mass more or less than 42 kg?

When we weight our body, a downward ward gravitational force acts

on it. Hence our actual mass is less than 42 kg

You have a bag of cotton and an iron bar, each indicating a

mass of 100 kg when measured on a weighing machine. In

reality, one is heavier than other. Can you say which one is

heavier and why?

In reality, a bag of an iron bar is heavier than a bag of cotton.Each

indicating a mass of 100 kg when measured on a weighing machine as

more gravitational force act on a bag of cotton due to its larger the

surface area.

In what direction does the buoyant force on an object immersed

in a liquid act?

Ans: The buoyant force acts on an object in the vertically upward

direction through the center of gravity of the displaced liquid. 

Why does a block of plastic released under water come up to

the surface of water?

A block of plastic released under water come up to the surface of

water because the up thrust or the buoyant force exerted by the water

is greater than the downward gravitational force. 

The volume of 50 gm of a substance is 20 cm3. If the density of

water is 1 g/cm3, will the substance float or sink?

Given the mass of the substance = 50 g     Volume of the substance =

20 cm3

Density of substance = Mass /Volume = (50 /20) g/cm3 = 2.5 g/cm3

Since the density of the substance 2.5 g/cm3 is greater than the

density of water (1 g/cm3), so the substance will sink in the water.

The volume of a 50 gm sealed packet is 350 cm3. Will the

packet float or sink in water if the density of water is 1 g/cm3 ?

What will be the mass of the water displaced by this packet  ?

Mass of packet = 500 g               Volume of packet = 350 cm3

Density of packet = Mass ÷ Volume = (500 / 350) g/cm3 = 1.43 g/cm3

The sealed packet will sink in the water as its density 1.43 g/cm3 is

more than that of water.

The volume of water that will be displaced by the packet = 350 cm3

And mass of this displaced water = Volume x Density = 350 x 1 = 350

gm.

State Archimedes’ principle. Give any two applications of

Archimedes principle?

Archimedes’ principle states that when a body is immersed partially

or fully in a fluid, it experiences an upward force that is equal to the

weight of the fluid displaced by it.

The two applications of Archimedes principle are given below:

(i) Floating of ships and submarines (ii) The lactometers to test purity

of milk

How do a submarine sink and float on water?

A submarine can both sink and float on water because of the ballast

tank . 

To make a submarine sink into the water, these tanks are filled with

water. This increases the weight of the submarine and it sinks.

To make a submarine float on the water surface, these tanks are

emptied by pumping out water from them. This decreases the weight

of the submarine and it floats

1. Even though stone also attracts earth towards itself, earth does not

move

(a) Because of greater mass of earth 

(b) Because of lesser mass of stone

(c) Force exerted by stone is less 

(d) Force exerted earth is large[1]

2. The weight of an object is :-

(a) Greater on earth and lesser on Moon 

(b) Lesser on earth and Greater on earth

(c) Equal on both earth and Moon 

(d) None of these[1]

3. Weight of an object has S.I, unit of :- 

(a) Newton 

(b) kg 

(c) N/Kg 

(d) Kg/N[1]

4. Which of the statements is correct?

(a) Mass is constant and weight is variable

(c) Both Mass and weight are variable

(b) Mass is variable and weight is constant. 

(d) Both Mass and weight are constant.[1]

5. State the Universal law of Gravitation?[2]

6. If heavier bodies are attracted more strongly by the earth, why do

they not fall faster to the ground?

7. State Archimedes Principle?[2]

8. A stone is dropped from the edge of the roof. It passes a window 2m

high is 0.1 s.How far is the roof above the window? [2]

9. The radius of earth is 6370Km and of mars is 3400 Km. If an object

weighs 200N or earth, what will be its weight on mars. The mass of

mars is 0.11 that of earth.[3]

10. Determine the value and units of universal Gravitational constant,

G?[3]

11. What is the up thrust experienced by a cube of edge – length 5cm

made of iron when completely immersed in ethanol of density 0.8

g/cm3 [3]

12. A stone is dropped from a height of 50m on earth. At the same

time, another stone  is thrown vertically upwards from the ground with

a velocity up wards from the ground with a velocity of 50m/s. At what

height from the ground will the two stones meet (g = -10 m/s2)

Reflection and Refraction Key concepts and terms

Work, Power, Energy MCQ for physics class 9

9th physics Thrust and Pressure, Archimedes’ Principle, Relative Density key point

Visitors Position

02 July 2011

CBSE Test Papers for Class 9 chapter Gravitation

1. Even though stone also attracts earth towards itself, earth does not

move

(a) Because of greater mass of earth 

(b) Because of lesser mass of stone

(c) Force exerted by stone is less 

(d) Force exerted earth is large[1]

2. The weight of an object is :-

(a) Greater on earth and lesser on Moon 

(b) Lesser on earth and Greater on earth

(c) Equal on both earth and Moon 

(d) None of these[1]

3. Weight of an object has S.I, unit of :- 

(a) Newton 

(b) kg 

(c) N/Kg 

(d) Kg/N[1]

4. Which of the statements is correct?

(a) Mass is constant and weight is variable

(c) Both Mass and weight are variable

(b) Mass is variable and weight is constant. 

(d) Both Mass and weight are constant.[1]

5. State the Universal law of Gravitation?[2]

6. If heavier bodies are attracted more strongly by the earth, why do

they not fall faster to the ground?

7. State Archimedes Principle?[2]

8. A stone is dropped from the edge of the roof. It passes a window 2m

high is 0.1 s.How far is the roof above the window? [2]

9. The radius of earth is 6370Km and of mars is 3400 Km. If an object

weighs 200N or earth, what will be its weight on mars. The mass of

mars is 0.11 that of earth.[3]

10. Determine the value and units of universal Gravitational constant,

G?[3]

11. What is the up thrust experienced by a cube of edge – length 5cm

made of iron when completely immersed in ethanol of density 0.8

g/cm3 [3]

12. A stone is dropped from a height of 50m on earth. At the same

time, another stone  is thrown vertically upwards from the ground with

a velocity up wards from the ground with a velocity of 50m/s. At what

height from the ground will the two stones meet (g = -10 m/s2)

1. Ramesh buys 6 bottles of syrup each containing 1litre. Each empty bottle weighs 400g. The density of syrup is 1.2 g/cm3. What weight does Ramesh have to carry home?

2. The volume of 900g of a substance is 1000 cm3. Will the substance sink or float in water if the density of water is 1g/cm3. What will be the mass of water displaced by the substance?

. 1. What The earth attracted to each other by gravitational force. Does the earth attract the moon, with a force that is greater, or smaller, or the force with which the moon attracts the earth? Why?

Q. 2. The earth attracts the moon. Does the moon attract the earth? If it does, why does the earth not move towards the moon?

Q. 3. How are ocean tides caused?

Q. 4. What do we call the gravitational force between the earth and your body?

Q. 5. The earth attracts an apple. Does the apple also attract the earth? If it does, why does the earth not move towards the apple?

Q. 6. Is the gravitational acceleration independent of mass? Name the experiment which concluded this?

Q. 7. Where do we observe the maximum value of the gravitational acceleration? Equator, poles or Mt Everest?

Q. 8. You must have seen two types of balances, one is the spring balance and the other is the one with the kabadiwalas. Which one of it would you use to measure the mass of an object? Why?

Q. 9. Why does a buffalo float on the river but not the man?

Q. 10. Why does ice float on the water?

Q. 11. Why does a ship made up of iron floats but the iron sinks?

Q. 12. How do submarines float or sink as desired?

Q. 13. Why does a mug full of water appear lighter inside the water?

Q. 14. A dead body floats in water with its head immersed in water. Explain?

Q. 15. In what direction does the buoyant force on an object, due to liquid act?

Q. 16. Why does a block of plastic piece left under water cone to the surface of water?

Q. 17. Write the condition under which the body would float on a liquid?

Reflection and Refraction Key concepts and terms

Work, Power, Energy MCQ for physics class 9

9th physics Thrust and Pressure, Archimedes’ Principle, Relative Density key point

Visitors Position

02 July 2011

CBSE Test Papers for Class 9 chapter Gravitation

1. Even though stone also attracts earth towards itself, earth does not

move

(a) Because of greater mass of earth 

(b) Because of lesser mass of stone

(c) Force exerted by stone is less 

(d) Force exerted earth is large[1]

2. The weight of an object is :-

(a) Greater on earth and lesser on Moon 

(b) Lesser on earth and Greater on earth

(c) Equal on both earth and Moon 

(d) None of these[1]

3. Weight of an object has S.I, unit of :- 

(a) Newton 

(b) kg 

(c) N/Kg 

(d) Kg/N[1]

4. Which of the statements is correct?

(a) Mass is constant and weight is variable

(c) Both Mass and weight are variable

(b) Mass is variable and weight is constant. 

(d) Both Mass and weight are constant.[1]

5. State the Universal law of Gravitation?[2]

6. If heavier bodies are attracted more strongly by the earth, why do

they not fall faster to the ground?

7. State Archimedes Principle?[2]

8. A stone is dropped from the edge of the roof. It passes a window 2m

high is 0.1 s.How far is the roof above the window? [2]

9. The radius of earth is 6370Km and of mars is 3400 Km. If an object

weighs 200N or earth, what will be its weight on mars. The mass of

mars is 0.11 that of earth.[3]

10. Determine the value and units of universal Gravitational constant,

G?[3]

11. What is the up thrust experienced by a cube of edge – length 5cm

made of iron when completely immersed in ethanol of density 0.8

g/cm3 [3]

12. A stone is dropped from a height of 50m on earth. At the same

time, another stone  is thrown vertically upwards from the ground with

a velocity up wards from the ground with a velocity of 50m/s. At what

height from the ground will the two stones meet (g = -10 m/s2)

Reflection and Refraction Key concepts and terms

Work, Power, Energy MCQ for physics class 9

9th physics Thrust and Pressure, Archimedes’ Principle, Relative Density key point

Visitors Position

02 July 2011

CBSE Test Papers for Class 9 chapter Gravitation

1. Even though stone also attracts earth towards itself, earth does not

move

(a) Because of greater mass of earth 

(b) Because of lesser mass of stone

(c) Force exerted by stone is less 

(d) Force exerted earth is large[1]

2. The weight of an object is :-

(a) Greater on earth and lesser on Moon 

(b) Lesser on earth and Greater on earth

(c) Equal on both earth and Moon 

(d) None of these[1]

3. Weight of an object has S.I, unit of :- 

(a) Newton 

(b) kg 

(c) N/Kg 

(d) Kg/N[1]

4. Which of the statements is correct?

(a) Mass is constant and weight is variable

(c) Both Mass and weight are variable

(b) Mass is variable and weight is constant. 

(d) Both Mass and weight are constant.[1]

5. State the Universal law of Gravitation?[2]

6. If heavier bodies are attracted more strongly by the earth, why do

they not fall faster to the ground?

7. State Archimedes Principle?[2]

8. A stone is dropped from the edge of the roof. It passes a window 2m

high is 0.1 s.How far is the roof above the window? [2]

9. The radius of earth is 6370Km and of mars is 3400 Km. If an object

weighs 200N or earth, what will be its weight on mars. The mass of

mars is 0.11 that of earth.[3]

10. Determine the value and units of universal Gravitational constant,

G?[3]

11. What is the up thrust experienced by a cube of edge – length 5cm

made of iron when completely immersed in ethanol of density 0.8

g/cm3 [3]

12. A stone is dropped from a height of 50m on earth. At the same

time, another stone  is thrown vertically upwards from the ground with

a velocity up wards from the ground with a velocity of 50m/s. At what

height from the ground will the two stones meet (g = -10 m/s2)

1. Ramesh buys 6 bottles of syrup each containing 1litre. Each empty bottle weighs 400g. The density of syrup is 1.2 g/cm3. What weight does Ramesh have to carry home?

2. The volume of 900g of a substance is 1000 cm3. Will the substance sink or float in water if the density of water is 1g/cm3. What will be the mass of water displaced by the substance?

. 1. What The earth attracted to each other by gravitational force. Does the earth attract the moon, with a force that is greater, or smaller, or the force with which the moon attracts the earth? Why?

Q. 2. The earth attracts the moon. Does the moon attract the earth? If

it does, why does the earth not move towards the moon?

Q. 3. How are ocean tides caused?

Q. 4. What do we call the gravitational force between the earth and your body?

Q. 5. The earth attracts an apple. Does the apple also attract the earth? If it does, why does the earth not move towards the apple?

Q. 6. Is the gravitational acceleration independent of mass? Name the experiment which concluded this?

Q. 7. Where do we observe the maximum value of the gravitational acceleration? Equator, poles or Mt Everest?

Q. 8. You must have seen two types of balances, one is the spring balance and the other is the one with the kabadiwalas. Which one of it would you use to measure the mass of an object? Why?

Q. 9. Why does a buffalo float on the river but not the man?

Q. 10. Why does ice float on the water?

Q. 11. Why does a ship made up of iron floats but the iron sinks?

Q. 12. How do submarines float or sink as desired?

Q. 13. Why does a mug full of water appear lighter inside the water?

Q. 14. A dead body floats in water with its head immersed in water. Explain?

Q. 15. In what direction does the buoyant force on an object, due to liquid act?

Q. 16. Why does a block of plastic piece left under water cone to the surface of water?

Q. 17. Write the condition under which the body would float on a liquid?

Reflection and Refraction Key concepts and terms

Work, Power, Energy MCQ for physics class 9

9th physics Thrust and Pressure, Archimedes’ Principle, Relative Density key point

Visitors Position

02 July 2011

CBSE Test Papers for Class 9 chapter Gravitation