Class 8

Karnataka Board Class 8 Science Chapter 12 Chemicals in Our Daily Life

KSEEB Class 8 Science Chapter 12 Textual Questions & Answers

I. Four alternatives are given to each of the following incomplete statement/ question. Choose the right answer.

Question 1.
Chlorine is prepared in the laboratory by the action of
a) Zn and HCl
b) MnO₂ + HCl
c) CaCO₃ and HCl
d) Pb(NO₃)₂ and HCl
Answer:
b) MnO₂ + HCl

Question 2.
The chief sources oils used to make soap are
a) petroleum products
b) coal+coke
c) animals and plants
d) soap and detergents
Answer:
c) animals and plants

II. Fill in the blanks :

Question 1.
MnO₂ + 4HCl → MnCl₂ +…………..
Answer:
Cl₂↑+ 2H₂O

Question 2.
Common name of sodium chloride is ……………….
Answer:
common salt

Question 3.
Chemical name of baking soda is …………….
Answer:
sodium chloride

III. Answer the following.

Question 1.
Pure and dry chlorine gas is collected by the upward displacement of air give reason.
Answer:
Chlorine gas collected by the upward displacement of air because chlorine is heavier than air.

Question 2.
Name the compound of chlorine

1. which is an anesthetic
2. which is used as a refrigerant
3. which is disinfectant
4. which is used to make pipes and tubes
5. which liberates chlorine on exposure to air.

Answer:

1. chloroform
2. chlorofluorocarbon (CFC)
3. Sodium chloride
4. polyvinyl chloride (PVC)
5. Calcium oxychloride

Question 3.
Mention four uses of chlorine.
Answer:
Chlorine is used in the manufacture of bleaching powder.

1. Chlorine is used in the manufacture of hydrochloric acid
2. It is used in the paper and pulp industry.
3. It is used as a bleaching agent and in the purification of water
4. It is used in the manufacture of polyvinyl chloride and Chlorofluorocarbons. (C.F.C)
5. Chlorine is used in the preparation of pesticides like benzene hexachloride commonly called BHC. dichloro diphenyl trichloroethane (DDT)
6. It is used in the preparation of chloroform which is used as an anesthetic.

Question 4.
Name the metal and the acid to be selected to prepare sulfur dioxide on the laboratory,
Answer:
To prepare sulfur dioxide in the laboratory copper turnings and sulfuric acid are used.

Question 5.
Name the acid formed when sulfur dioxide dissolves in water.
Answer:
When sulfur dioxide dissolves in water sulfurous acid is formed.

Question 6.
Give two uses of sulfur dioxide.
Answer:
Sulfur dioxide is used in the manufacture of sulfuric acid

1. It is used to increase the shelf life of foods.
2. In the sugar industry, sulfur dioxide is used to remove coloring matter from sugar.
3. It is used to prevent the decolonization of dried fruits.

Question 7.
Mention any two differences between soap and synthetic detergents.
Answer:
Soap

1. prepared from vegetable oil or animal fat
2. biodegradable
3. Not good for washing, when the water is hard
4. does not cleanse well in acidic medium

Detergents

1. made from hydrocarbons obtained from petroleum
2. non-biodegradable
3. cleanse well even in hard water
4. cleanse well even in acidic medium.

Question 8.
How is detergent industrially manufactured?
Answer:
A method of manufacturing detergents: A long chain hydrocarbons obtained from petroleum are treated with concentrated sulfuric acid. Then it is neutralized with sodium hydroxide the sodium salt thus obtained is detergent.

Question 9.
Why are detergents better than soap in cleaning action?
Answer:
Soap does not give lather with hard water. The soap reacts with the salts present in the hard water to form insoluble precipitates which hinder the cleaning action whereas detergents give lather with hard water and do not form an insoluble scum.

KSEEB Class 8 Science Chapter 12 Additional Questions & Answers

Question 1.
Mention the chemical name of common salt.
Answer:
The chemical name of common salt is sodium chloride. (NaCl)

Question 2.
Name the common element present in bleaching powder and common salt?
Answer:
Chlorine is the common element present in bleaching powder and common salt.

Question 3.
Name the minerals of chlorine.
Answer:
The most common minerals of chlorine are Halite, (rock salt), sylvite carnallite, chlorapatite.

Question 4.
How is chlorine manufactured industrially?
Answer:
In industry, chlorine is produced by passing an electric current through an aqueous solution of sodium chloride or through molten sodium chloride. The products produced along with chlorine are sodium hydroxide and hydrogen.

Question 5.
What is aqueous solution?
Answer:
Solutions made using water are called aqueous solution.

Question 6.
Explain the preparation of chlorine in the laboratory.
Answer:

Take nearly 20 g of manganese dioxide in the flask add concentrated hydrochloric acid to it through thistle funnel so that tip of the thistle funnel is dipped in the acid. Heat the flask. The gas liberated. The liberated gas is collected in the jar by the upward displacement of air.
MnO₂ + 4HCl → MnCl₂ + Cl₂ ↑+ 2H₂O

Question 7.
Explain the preparation of chlorine gas from potassium permanganate and con. HCl.
Answer:

Take potassium permanganate in the flask, Add concentrated Hydrochloric acid through the droping Funnel chlorine gas is bi berated. The liberated gas is collected in separated bottles by the upward displacement of air.

Question 8.
Write the physical properties of chlorine are.
Answer:
The physical properties of chlorine are.

1. Chlorine is pale greenish-yellow in colour.
2. It is a supporter of combustion.
3. It is heavier than air.
4. It turns blue litmus red therefore acidic.

Question 9.
Mention the chemical properties of chlorine.
Answer:
The chemical properties of chlorine.

1.  Burning magnesium ribbon react with chlorine to form magnesium chloride.
   Mg + Cl₂ → MgCl₂
2. Chlorine reacts with hot red phosphorous giving phosphorus pentaxide
   2p + 3Cl₂ → 2PCl₃ (Limited supply of chlorine)
   2p + 5Cl₂ —» 2PCl₅ (Excess supply of chlorine)
3. Sodium burns vigorously on chlorine with golden yellow flame to form sodium chloride.
   2Na + Cl₂ → 2NaCl
4. When heated aluminium powder is sprinkled into jar of chlorine it burns brightly with flashes of light.
   2Al + 3Cl₂ → 2AlCl₃
5. Chlorine reacts with water to form hypochlorous acid.

Question 10.
Write a short note on the Historical use of chlorine.
Answer:
Chlorine was first used in the sterilization of drinking water to control the spread of water-borne diseases such as typhoid. Cholera, dysentery, and gastro-enteritis which killed people more than the people who were killed in all wars in history.

Question 11.
Write the chemical name of bleaching powder? How it is prepared?
Answer:
The chemical name of bleaching powder is calcium oxychloride. Molecular formula of bleaching powder (Calcium oxychloride) is CaOCl_2. It is prepared by passing chlorine gas into slakes lime at 4Q0°C.
Ca(OH)₂ +4Cl₂ → CaOCl₂ + H₂O

Question 12.
Mention the food items which contain sulfur.
Answer:
Garlic, onion, reddish, cauliflower, Egg, yolk.

Question 13.
Name parts of the Human body which contain sulfur.
Answer:
Hair, nails, and skin contain sulfur.

Question 14.
Write a short note on the Discovery of sulfur dioxide.
Answer:
Priestley prepared sulfur dioxide in the year 1774 by heating concentrated sulfuric acid with mercury and called it “vitriolic acid air.

Question 15.
Write the methods by which sulfur dioxide can be manufactured on a large-scale.
Answer:
Method 1
Sulfur is present in many minerals one of the minerals is mercurous sulfide. It is commonly called cinnabar. The ”
sulfide burns in the presence of air and sulfur dioxide are obtained as a by-product.
HgS+O₂ → Hg + SO₂ ↑

Method 2
During the extraction of zinc from zinc blend. Sulfur dioxide is obtained as a byproduct.
2ZnS+ 3O₂ → 2ZnO+ 2SO₂↑

Question 16.
Write the laboratory preparation of sulfur dioxide.
Answer:

Set up the apparatus as in the figure. Take copper turning in the flask. Add concentrated sulfuric acid to it through thistle Funnel. Heat the flask Sulfur dioxide gas can be collected in the jar.
Cu + 2H₂SO₄ → CuSO₄+ SO₂ + 2H₂O

Question 17.
Mention the physical properties of sulfur dioxide.
Answer:
The physical properties of sulfur dioxide are

1. It is Colorless
2. It is has a pungent smell
3. It is – Not a supporter of combustion
4. It is – Turns blue litmus red therefore acidic

Question 18.
What is Acid rain? Mention, its effects.
Answer:
Water molecules in the atmosphere react with sulfur dioxide to form acid rain.
SO₂+ H₂O → H₂SO₃ The effects are :

1. Acid rain corrodes monuments, statues and buildings.
2. It affects the soil fertility and effects plants growth.

Question 19.
What happens when a burning magnesium ribbon is kept inside a jar containing sulfur dioxide gas?
Answer:
Magnesium containing to burn displacing sulfur particles which stick to the jar
2Mg + SO₂ → 2MgO+ S

Question 20.
How is baking soda manufactured?
Answer:
Baking soda is manufactured by passing carbon dioxide through saturated sodium carbonate solution in water.
Na₂CO₃ + CO₂ + H₂O→ 2NaHCO₃

Question 21.
Write the uses of baking soda.
Answer:
Uses of baking soda

1. It is used in bakery to make the bakery items.
2. It is used in medicine which acts ‘ as antacid, to treat excess of acid formed in the stomach.
3.  It is used as a mild cleaning agent
4. It is used to prepare aerated water (soda water)

Question 22.
What is soap? Mention the raw materials used to make soap.
Answer:
A cleaning substance made from animal fats or vegetable oil is called soap. The raw materials are, oil or fat, sodium hydroxide or potassium hydroxide, and common salt.

Question 23.
Explain the method of preparation of soap.
Answer:
The mixture of fats and sodium hydroxide is allowed to boil in the kettle using the steam within the kettle. After boiling, the mass thickness as the fat reacts with sodium hydroxide producing soap and glycerin. Salt is added to separate soap from glycerin.

The soap forms its layer at the top and the glycerin settles at the bottom the glycerin is taken out from the bottom of the kettle. Soap is taken off from the top the soap is then cooled.
Oil/Fat + Sodium hydroxide → Soap + glycerol.

Question 24.
What is glycerol? Mention the uses.
Answer:
Glycerol or glycerin is a sweet viscous liquid soluble in water. Uses of Glycerol are :

1. It is used in the manufacture of explosives, elastics, and pharmaceuticals.
2. It is also used to prevent freezing.

Question 25.
Overuse of synthetic detergents cause water pollution why? Give reason.
Answer:
Overuse of synthetic detergents cause water pollution because detergents are non-biodegradable.

Question 26.
What are detergents?
Answer:
A cleaning substance which is made using petroleum is called detergents.

Question 27.
How is liquid soap prepared?
Answer:
A method of manufacturing liquid soap. Heat the mixture of oil and potassium hydroxide solution. Stir well. As the soap cooks it will be converted to the gel phase. Add distilled water and stir well and add little scent, liquid soap is ready.

KSEEB Solutions for Class 8 Science

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Class 8 Science Jalagola Additional Questions and Answers

You can Download No Men are Foreign Poem Questions and Answers Pdf, Notes, Summary KSEEB Solutions for Class 8 English to help you to revise complete Syllabus and score more marks in your examinations.

No Men are Foreign Poem Questions and Answers, Notes, Summary

C1. Answer the following questions and share your responses with your partner:

Question 1.
What does the poet remind us of in the first line of the poem?
Answer:
The poet reminds us that no man is a stranger and no country is a foreign country. All men are the same wherever we go, and all countries are like our own country.

Question 2.
What according to the poet, are we doing when we hate others?
Answer:
According to the poet, we should remember that whenever we are told to hate our brothers, it is ourselves that we shall hate, dispossess, betray, and condemn.

Question 3.
What are the two bad effects of war? Read lines 16 to 19 and answer.
Answer:
If we fight or war against each other it affects the earth and air. The two bad effects are

1. The earth and air will become impure.
2. Hatredness between brothers increases.

Read and Write:

C2. Read and discuss your responses with your partner. Then write:

Question 1.
How do you think we are all treated alike by nature?
Answer:
Nature has given the same physical features and mental abilities to all the people living on earth. It has provided all the natural resources like sun, air and water to the people. People work hard to cultivate lands and produce food in all parts of the world. In each and every part of the earth people lead a common life. There is no discrimination in nature.

Question 2.
Read the third stanza carefully. What message does the poet want to convey to us?
Answer:
People living in different parts of the earth do have eyes like ours – the eyes that help us to wake up in the morning and sleep at night. They have the ability to love and bring about oneness among people. We can see people living a common life wherever we go. Therefore, we should develop a sense of equality and brotherhood among ourselves.

Question 3.
Do you agree with the poet that we should wage no war? How do you justify that?
Answer:
Yes, all should agree with the poet. Because war gives way for hatred ness only. There is no end for this so we should not wage war. The poet mentions in the following line. “To hate our brothers, it is ourselves that I shall dispossess, betray, condemn. It is the j human earth that we defile. Our hells of fire I and dust outrage the innocence of air that an everywhere our own.

Question 4.
Some are of the opinion that the poet might have written this poem after witnessing the bad effects of the Second i World War. Mention some of the lines in the poem to support that opinion
Answer:
The opinion of people about the time of writing this poem might be true. The following lines have a reference to soldiers, war, and its evil effects:

1. Beneath all uniforms, a single body breathes
2. Are fed by peaceful harvests, by war’s long winter started
3. Remember, we who take arms against each other
4. Our hells of fire and dust outrage the innocence.

Question 5.
Briefly describe how a war spoils everything.
Answer:
People living in different parts of the earth have isolated themselves on the basis of colour, race, creed, language and country. Though they are all human beings basically, they wage war against one another in the name of race, religion and other factors. Each country wants to establish supremacy over the others.

As a result there is mass destruction. With the use of modern weaponry, lakhs of people are killed, their homes, fertile lands are reduced to ashes. If we recall the devastating effects of the Second World War, we can realize that war brings a lot of misery to the people.

No Men Are Foreign MCQ Question.

No Men are Foreign Additional Questions and Answers

Question 1.
What does a peaceful harvest refer to?
Answer:
Peaceful harvest refers to peacetime and the prosperity one has in times of peace.

Question 3.
What are the hells of fire and dust? What do they destroy?
Answer:
Hells of fire and dust are the fire, smoke, and dust from bombs and gunfire. They pollute the air which was given by God to all in pristine purity. The poet reminds us that we have no right to spoil what is commonly owned by all children of God.

Question 5.
What does the poet emphasise by beginning and ending the poem with the same line?
Answer:
When a word, phrase, clause, or sentence is repeated, the repetition is for the emphasis. The poet’s intention is to drive home the truth that thinking of people of foreign countries as strangers is an unnecessary man-made barrier that should be broken.

Question 7.
War is the enemy of our environment. How?
Answer:
When we fight a war and use dreadful weapons against others, we pollute our environment with the dust and the smoke of the guns.

Question 9.
What happens when war breaks out?
Answer:
When we wage war and use dreadful weapons against, others, we defile our own earth. The dust and smoke of guns pollute the very air we breathe.

Question 11.
What are the evils of war, according to the poet?
Answer:
The poet advises people to shun hatred and warfare. The poet says that during peace, people enjoy the harvests and prosper, whereas during war people experience distress and scarcity of food. He further says that when we hate others, we actually rob, deceive and condemn ourselves. When we fight against others we defile the purity of our own earth. The fire and smoke from the weapons of war poison the air which we all breathe and is essential for our existence.

Comprehension:

Read the following extracts and answer the questions that follow:

Question 1.
Remember, no men are strange, no countries foreign Beneath all uniforms, a single body breathes Like ours; the land our brothers walk upon Is earth like this, in which we all shall lie.

1. Who is the narrator in the poem? To whom is the poem – addressed?
2. What is there beneath all uniforms?
3. Who are referred to as brothers?

Answer:

1. The narrator in the poem is a person who believes in the idea of universal brotherhood. He addresses other Citizens of the world.
2. Beneath the uniforms all men are the same, they are all creations of God, breathing alike.
3. Brothers are fellow human beings.

Question 3.
They, too, aware of sun and air and water,
Are fed by peaceful harvests, by war’s long winter starv’d.
Their hands are ours, and in their lines we read
Labour not different from our own.

1. Who are ‘they’ that are mentioned in the extract?
2. What are peaceful harvests?
3. In what way is starvation associated with winter?
4. What is meant by, ‘Their hands are ours’?

Answer:

1. ‘They’ refers to foreigners.
2. Peaceful harvest refers to peacetime and the prosperity one has in times of peace.
3. Wintertime is associated with cessation of activity and end of productivity. The time of war is as bleak as the time of winter. Life comes to a standstill and people die of starvation at the time of war.
4. When the poet says, “Their hands are ours”, he means to suggest the idea that people all over the world work in the same manner as their aspirations are the same.

Question 5.
Their hands are ours, and in their lines we read
A labour not different from our own.
Remember, they have eyes like ours that wake
Or sleep, and strength that can be won
By love. In every land is common life
That all can recognize and understand.

1. Why does the poet allude to the similarity of hands of all human beings?
2. Why does the poet say that human ‘strength’ can be won by love?
3. What do you mean by common life? flow is it the same everywhere?
4. What is the message conveyed by the poet?

Answer:

1. People living in other countries have the same hands as we. They, too, are destined to labour for earning their livelihood as we are.
2. The poet wants to say that love has the emotional strength and power to subdue the most powerful person in the world.
3. The poet means to say that people all over the world lead a common life. Life is the same everywhere because people all over the world wake up and sleep in the same manner.
4. The poet conveys a message of universal brotherhood.

Question 7.
Remember, we who take arms against each other It is the human earth that we defile.
Our hells of fire and dust outrage the innocence Of air that is everywhere our own.
Remember, no men are foreign, and no countries strange.

1. What are the harmful effects of waging war against others?
2. What are the hells of fire and dust? What do they destroy?
3. What is the innocence of air? How is it defiled?
4. How is war the enemy of our environment?

Answer:

1. When we wage war and use dreadful weapons against others, we defile our own earth. The dust and smoke of guns pollute the very air we breathe.
2. Hells of fire and dust are the fire, smoke and dust from bombs and gunfire. They pollute the air which was given by God to all in pristine purity. The poet reminds us that we have no right to spoil what is commonly owned by all children of god.
3. Innocence of air is the purity of air. It is defiled by the guns and bombs used in wars. In other words, the innocence of air is spoilt by the wickedness of man. The poet seems to suggest that all gifts of God are pure and any act of defilement is evil.
4. When we fight war and use dreadful weapons against others, we pollute our environment with the dust and the smoke of the guns.

Multiple Choice Questions:

Four alternatives are given for each of the following questions/incomplete statements. Choose the most appropriate one.

Question 1.
The poem ‘No Men are Foreign’ is written by
A) James Kirkup
B) Henry Wotton
C) Isaac Watts
D) Sarojini Naidu
Answer:
A) James Kirkup

Question 3.
‘Hells of fire and dust’refer to
A) destruction of hell
B) fire, smoke and dust from bombs and gunfire
C) the burning down of hell
D) war that takes place in hell.
Answer:
B) fire, smoke and dust from bombs and gunfire

Question 5.
The force that can win over others’ strength is
A) war
B) love
C) hatred
D) peaceful harvests
Answer:
B) love

Question 7.
If we take up arms against each other
A) there will be war
B) there will be destruction
C) there will be fire and dust in hell
D) we defile the earth
Answer:
D) we defile the earth

No Men are Foreign Poem Summary in English

The authors intended to write this poem is universal brotherhood. According to him all men in the universe are the same and equal. So he is asking us to behave that nobody is stranger and no country is foreign because ail are alike. Though we all look different, we are all having same body. Similarly, the earth where we live and die is same. The Sun, air, and water are all same. We should live with peace it brings prosperity. War brings adversity, it means great suffering for long time. All hands are same and the lines in tire hands are also same. The labor is also not different.

We should remember that all are having same eyes with which we can sleep or awake. We can won all by love. All things should be possible by love. In every way life is common. That all can recognize and understand.

We should remember that whenever we are star hate our brothers, it is our fault. We have no right to condemn others. At the same time we have no right to look down upon anybody or discriminate, against anybody on any grounds. The poet makes a strong plea against the evils of war. By taking up arms, men violate the sanctity of the earth, polluting it with not only dust and smoke, but also hatred. Men must learn to develop a feeling of universal brotherhood. Men must learn that no man is stranger and no country is foreign.

No Men are Foreign Poem Summary in Kannada

Karnataka Board Class 8 Science Chapter 8 Describing Motion

KSEEB Class 8 Science Chapter 8 Textual Questions & Answers

I. Four alternatives are given to each of the following incomplete statement/ question, choose the right answer.

Online Circular Velocity Calculator tool makes the calculation faster, and it shows the result in a fraction of seconds.

Question 1.
Uniform circular motion is called continuously accelerated motion mainly because
(a) direction of motion changes
(b) Speed remains the same
(c) Velocity remains the same
(d) direction of motion does not change
Answer:
a) direction of motion changes

Question 2.
A cricketer hits a sixer, the cricket ball moves up with a velocity of 2 ms^-1 and falls down. Its initial velocity while falling down will be
a) 1 ms^-1
b) 1 ms^-2
c) 0 ms^-1
d) 2 ms^-1
Answer:
c) 0 ms^-1

II. Fill in the blanks with suitable words:

Question 1.
S.I. unit of acceleration is ………….
Answer:
meter per second²/ms^-2

Question 2.
Velocity has both speed and ……….
Answer:
direction

Question 3.
If an object starts from A and comes back to A. It displacement will be ………….
Answer:
(0) zero

III. Solve

Questions 1.
An object is moving in a circular path of radius 3.5 m. If completes one full cycle, what will be the displacement and what is the distance traveled?
Answer:
radius = 3.5 m
starting point is A and ending point also A.
the displace = 0
Distance traveled = π × 3.5 × 2

Question 2.
An object changes its velocity from 30 ms^-1 to 40 ms^-1 in a time interval of 2 seconds what is its acceleration?
Answer:
u = 30 ms^-1
v = 40 ms^-1
t = 2 sec
a = ?

Question 3.
An object at rest starts moving. It covers a distance of 2 m in one second. It covers a, further distance of 5 m in two seconds in the same direction what is the average velocity and acceleration?
Answer:
distance traveled on 1 sec = 2 mts
distance traveled on 2 sec = 5 mts
total distance traveled = 2 + 5 = 7 mts
total time taken to cover 7 mts = 1+2 = 3 sec

= \(\frac { 7 }{ 3 }\) = 2.3 ms^-1
Average velocity = 2.3 ms^-1
s = ut + \(\frac { 1 }{ 2 }\) at²
7 = 0  3 +\(\frac { 1 }{ 2 }\) a × 3²
7 =0 + \(\frac { 1 }{ 2 }\) a × 9
= \(\frac { 9 }{ 2 }\) a = 7
9a =7 × 2 = 14
a =  \(\frac { 14 }{ 9 }\)  = 1.5 ms^-2

IV. Answer the following.

Question 1.
If a body is moving with uniform velocity in a given direction its acceleration will be zero, why?
Answer:
The acceleration will be zero in the above situation since there is no change in velocity in unit time.

Question 2.
Distinguish between speed and velocity.
Answer:

1. Speed
   • Speed is the distance traveled by an object in unit time
   • Speed = \(\frac { distance }{ time }\)
   • Speed is a scalar quantity
   • Speed has the only magnitude
2. Velocity
   • Velocity is the rate of displacement of the body in unit time.
   • Velocity =\(\frac { displacement }{ time }\)
   • Velocity is a vector quantity
   • It has both magnitude and direction.

Question 3.
Distinguish between distance traveled and displacement.
Answer:

1. Distance traveled
   • Distance traveled is the length of actual path traveled by a body from one position to another.
   • It is a scalar quantity
   • It has an only numerical value
2. Displacement
   • Displacement is the shortest path between initial and final position of the moving body.
   • It is a vector quantity
   • If has both numerical value and direction.

Question 4.
What are uniform and non-uniform speed?
Answer:

1. If an object covers equal distance in equal intervals of time, it is said to be uniform motion.
2. non-uniform motion: If an object covers unequal distance in equal intervals of time, it is said to be non uniform motion.

Question 5.
While mentioning acceleration the time is mentioned two times, why?
Answer:
Velocity is the rate of displacement of a body in unit time.
V =\(\frac { displacement }{ time }\)
Acceleration is the change in velocity of a body in unit time.

While mentioning acceleration time is mentioned two times. (Acceleration occurs twice)

V. Extended activity
Represent the following motion by a graph.

Question 1.
Find the acceleration
Ans. Acceleration from the graph
= \(\frac { 40-10 }{ 4-1 }\) = \(\frac { 30 }{ 3 }\) = 10 ms^-1

Question 2.
Find the time taken when the velocity in 35 ms^-1
Answer:
Time taken to travel a distance of 35 ms^-1  is 1.5 seconds.

KSEEB Class 8 Science Chapter 8 Additional Questions & Answers

Question 1.
Define motion?
Answer:
The change in position of a body with time when compared with that of another body is called motion.

Question 2.
Motion is reflective-substantiate this statement with a suitable example.
Answer:
Imagine that you are sitting inside the train when the train starts moving you a fee that the persons on the platform are moving backward you feel that you and the other persons inside the train are not moving.
But for a person standing outside the train, the feeling will be that the train, you and the other members inside the compartment are all moving.

Question 3.
An object travels from A to B and then from B to C as shown in the figure.
1. Find the distance traveled and
2. Find the displacement
3. Write the conclusion
Answer :

Let ABC is a right-angled triangle with B as shown in the actual figure,

1. If a person travels from A to B and then to C the total distance traveled is = (3 m + 4 m) = 7 mts.
2. The displacement is the change in position from A to C
   
3. displacement value is lesser than the distance traveled.

Question 4.
An object moves from A to A in a circular path of radius 7 m. What is the distance traveled? What is the displacement?
Answer:
Displacement = Diameter = 2 × radius = 2 × 7= 14 m
Distance traveled = \(\frac { 1 }{ 2 }\) × circumference
= \(\frac { 1 }{ 2 }\) × 2 × π × r
= \(\frac { 1 }{ 2 }\) × 2 × \(\frac { 22 }{ 7 }\) × 7
= 22 m

Question 5.
Define the following
a) Speed
b) Velocity
Answer:

1. Speed: is the distance traveled by an object in unit time
2. Velocity: is the rate of displacement of a body in unit time.

Question 6.
An object is moving in a circular path of radius 7 m. To travel from ‘A’ to ‘B’ along the circumference it takes 2 seconds?
Answer:
Data : radius = 7 m
time = 2 s
average speed = ?
speed = \(\frac { distance traveled }{ time }\)

Question 7.
When can we say that speed and velocity are synonyms.
Answer:
Speed and velocity will be equal for uniform motions along a straight line. Then it will be one and the same.

Question 8.
What is meant by acceleration?
Answer:
A change in velocity of a body in unit time or the rate of change of velocity is called acceleration.

Question 9.
For an object moving at a uniform speed in a circular path, though the speed is uniform it is continuously accelerated, why? Give reason.
Answer:.
For an object moving in a circular path, the direction is changing at every point even though the speed is the same. Therefore velocity changes and hence it is continuously accelerated.

Question 10.
An object at rest gains an average velocity of 40 ms-1 in 5 seconds. What will be its acceleration?
Answer:
Its initial velocity, u = 0
Its final velocity, v = 40 ms^-1
Time taken t = 5 second the
rate of change of velocity
\(\frac { 40 }{ 8 }\) = 8 ms^-2
acceleration, a = 8 ms^-2

Question 11.
An object at rest starts moving and attains a velocity of 10 ms^-1 after 5 seconds. What is the acceleration?
Answer:
Initial velocity, u = 0
Final velocity, v = 10 ms^-1
Time interval, t = 5 second
a = \(\frac { u-v }{ t }\) = \(\frac { 10 – 0 }{ 5 }\) = 2 ms^-2

Question 12.
An object moving with a uniform velocity of 10 ms^-1 comes to rest after 5 seconds. What is the acceleration?
Answer:
Initial velocity, v = 10 ms^-1
Final velocity, u = 0
Time interval, t = 5 second
a = \(\frac { u-v }{ t }\) =  \(\frac { 0 – 10 }{ 5 }\) = – 2 ms^-2

Question 13.
An object at rest starts moving with a uniform acceleration of 1 ms^-2 Calculate the distance traveled by it in 4 seconds.
Answer:
u = 0
a = 1 ms^-2
t = 4 second ,
Distance traveled s = ut + \(\frac { 1 }{ 2 }\) at²
S = 0 × 4 + \(\frac { 1 }{ 2 }\) × 1  × 4²
=0 + \(\frac { 1 }{ 2 }\) × 1 × 16 = 18 m

Question 14.
An object starts from rest and attains a uniform acceleration of 4 ms^-2 what will be its velocity at the end of half a meter?
Answer:
u = 0
a = 4 ms^-2
s = \(\frac { 1 }{ 2 }\)
v² = ?
v²= u² + 2as
v² = 0² + 2 × 4² × \(\frac { 1 }{ 2 }\)
v² = 4
v² = \(\sqrt { 4 } \) = 2 ms^-1

Question 15.
What is the distance-time graph? What are its uses?
Answer:
Motion can be represented by a time graph. If it represents time on the x-axis and distance traveled on the y-axis, it is called a distance-time graph.

Uses of the distance-time graph are,

1. The distance at which the body is at present from its starting point can be found out.
2. Time taken to cover a definite distance can be determined
3. Since it is uniform motion speed of the body can also be calculated.

Question 16.
What do you infer about the velocity when the velocity-time graph is parallel to the x-axis.
Answer:
The body is at rest no acceleration.

Question 17.
Define negative acceleration?
Answer:
It is a Negative acceleration as the moving body reduces its velocity due to applied force, denoted by “-a”.

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