Std.VII- Motion,Force and Work (Question&Answers)

Question 1:

Fill in the blanks with the proper words from the brackets.
(stationary, zero, changing, constant, displacement, velocity, speed, acceleration, stationary but not zero, increases)
(a) If a body traverses a distance in direct proportion to the time, the speed of the body is ............... .
(b) If a body is moving with a constant velocity its acceleration is .......... .
(c) .............. is a scalar quantity.
(d) ............. is the distance traversed by a body in a particular direction in unit time.

ANSWER:

(a) If a body traverses a distance in direct proportion to the time, the speed of the body is constant.
(b) If a body is moving with a constant velocity its acceleration is zero.
(c) Speed is a scalar quantity.
(d) Velocity is the distance traversed by a body in a particular direction in unit time.

Page No 50:

Question 2:

Observe the figure and answer the questions.

Sachin and Sameer started on a motorbike from place A, took the turn at B, did a task at C, travelled by the route CD to D and then went on to E. Altogether, they took one hour for this journey. Find out the actual distance traversed by them and the displacement from A to E. From this, deduce their speed. What was their velocity from A to E in the direction AE? Can this velocity be called average velocity?

ANSWER:

.

Page No 50:

Question 3:

From the groups B and C, choose the proper words, for each of the words in group A.
 

A	B	C
Work	Newton	erg
Force	Metre	cm
Displacement	Joule	dyne

ANSWER:

A	B	C
Work	Joule	erg
Force	Newton	dyne
Displacement	Metre	cm

Page No 50:

Question 4:

A bird sitting on a wire, flies, circles around and comes back to its perch. Explain the total distance it traversed during its flight and its eventual displacement.

ANSWER:

The total distance travelled by the bird during its flight = 2×$\times$(Distance between the point where the bird was sitting and the point from where it takes a turn)
The eventual displacement of the bird is zero as it returns to its initial point i.e. where it was sitting.

Textbook Page No 50:

Question 5:

Explain the following concepts in your own words with everyday examples : force, work, displacement, velocity, acceleration, distance.

ANSWER:

Force: It is any kind of push or pull on a body due to another body when the bodies interact with each other. It is a vector quantity. For example, a person applies a force in the form of push or pull to open a door.

Work: It is defined as the work done by a force that causes a displacement in an object. It is a scalar quantity. For example, a child does work when he drags a toy car on the ground.

Displacement: It is the shortest distance between the initial and final position of an object. It is a vector quantity. For example, when we go to a mall for shopping from our house and then return to the house, the displacement would be 0 as our initial position (house) and final position (house) is same.

Velocity: Velocity is defined as the rate of change of displacement. It is a vector quantity. For example, a car running on a straight road has some velocity.

Acceleration: The rate of change of velocity is known as acceleration. It is a vector quantity. For example, if a car is moving on a straight with variable speed, it will posses some acceleration. In case the speed of the car remains same bu

 the direction of car changes, then also the car would be accelerating.

Distance: It is the actual path length covered by an object during its motion. It is a scalar quantity.  For example, when we go to a mall for shopping from our house and then return to the house, the distance travelled by us would be twice the distance between our house and the mall.

Page No 50.

Textbook Page No 50:

Question 7:

Solve the following problems.
(a) A force of 1000 N was applied to stop a car that was moving with a constant velocity. The car stopped after moving through 10 m. How much is the work done?
(b) A cart with mass 20 kg went 50 m in a straight line on a plain and smooth road when a force of 2 N was applied to it. How much work was done by the force?

ANSWER:

(a) Work done by the force to stop the car=

F×S=1000×10=10000 J $\mathrm{Work} \mathrm{done} \mathrm{by} \mathrm{the}$

$\mathrm{force} \mathrm{to} \mathrm{stop} \mathrm{the} \mathrm{car}=F\times S=1000\times 10=10000 \mathrm{J}$

(b) Work done by the force=F×S=2×50=100 J$\mathrm{Work} \mathrm{done} \mathrm{by} \mathrm{the} \mathrm{force}=F\times S=2\times 50=$100 J

Std.7 Science Ch.5.Food Safety

Question 1:

Complete the following statements by using the correct option from those given below.
(Irradiation, dehydration, pasteurization, natural, chemical)
(a) Drying the food grains from farms under the hot sun is called .......... .
(b) Materials like milk are instantly cooled after heating up to a certain high temperature. This method of food preservation is called .......... .
(c) Salt is a .......... type of food preservative.
(d) Vinegar is a .......... type of food preservative.

ANSWER:

(a) Drying the food grains from farms under the hot sun is called do dehydration.
(b) Materials like milk are instantly cooled after heating up to a certain high temperature. This method of food preservation is called pasteurization.
(c) Salt is a natural type of food preservative.
(d) Vinegar is a chemical type of food preservative.

Question 2:

Answer the following questions in your own words.
(a) How is milk pasteurized?
(b) Why should we not consume adulterated food materials?
(c) What precautions do your parents take to keep foodstuffs safe?
(d) How does food spoilage occur? Which are the various factors spoiling the food?
(e) Which methods of food preservation would you use?

ANSWER:

(a) How is milk pasteurized?

a. Milk is pasteurised in order to kill any kind of harmful microorganism present in it and to increase its shelf life. Pasteurisation is a process in which the milk is heated to a certain temperature for a fixed period of time and then is quickly cooled. For example, it may be heated at 80^oC for 15 minutes and then immediately cooled. This helps to kill any kind of microorganism which is present in milk. 

(b) Why should we not consume adulterated food materials?
b. The process of substituting or concealing the quality of food, adding harmful or poisonous substances to food, and misbranding or giving false labels to food is known as food adulteration. the adulterants which are added to food products have harmful effects on our bodies. For example:

• vegetable oil is adulterated with cheaper and non-edible oils such as argemone oil which causes dropsy, which in turn leads to renal and cardiac failure.
• pulses are mixed with kesari dal or with metanil yellow to improve the colour which can cause carcinogenic disorder and it can also affect the nervous system.

We should be very careful in buying our food products and should be aware of our rights and actions which can be taken against people who are involved in this crime.

(c) What precautions do your parents take to keep foodstuffs safe?
Answer:Precautions which are taken to preserve foods:

1. Storing fruits and vegetables in proper storage, for example, fruits like bananana are not stored in refrigerator while fruits like mangoes require refrigerator.
2. Storing grains, dals etc. in dry conditions and in air proof containers.
3. Making pickles and jams to increase their shelf life.

(d) How does food spoilage occur? Which are the various factors spoiling the food

Ans:. The undesirable or disagreeable change in the state of food which makes it unsuitable for human and animal consumption is termed as food spoilage. Spoilage of food can be caused by various factors like:

• Microorganisms: Growth of microorganisms like bacteria, fungi etc. can lead to spoilage of food. 
• Action of enzymes: Enzymes which are an inherent part of plant and animal tissue begin the decomposition process after the death of plant or animal. For example, a bananana starts to ripen and then spoil if it is not consumed on time.
• Infestation by insects: Insects like cockroaches may infest the food stuff and make them unsuitable for consumption. There is possiblity of transmission of pathogens from these insects.
• Wrong handling of products may also result in the spoilage of foodstuffs.
• Overcooking is another such reason for spoilage of foods.

(e) Which methods of food preservation would you use?
Answer:The following methods of food preservation can be used:

• Preservation by common salt: Common salt is usually used to preserve meat and fish as it checks the growth of bacteria in these foods. It is also used to preserve amla, raw mangoes, and tamarind.

• Preservation by sugar: Sugar is usually used to preserve jam, jellies, and squashes. Sugar prevents spoiling of food by reducing the moisture content of food, which inhibits the growth of bacteria in it.

• Preservation by oil and vinegar: Oil and vinegar are used to preserve vegetables, fruits, fish, and meat. They prevent food from getting spoilt as micro-organisms cannot grow in such an environment.

Question 3:

What shall we do?
(a) There are vendors selling uncovered sweetmeats in open places in the market.
(b) A 'pani-puriwalla' is serving the pani puri with dirty hands.
(c) We have purchased a large quantity of fruits and vegetables.
(d) We need to protect foodstuffs from pests like rats, cockroaches, wall-lizards, etc.

ANSWER:

a. We should not eat food from vendors who sell uncovered foods. We should try to talk to him and convince him to keep his food covered while selling it. Also, we should tell him the importance of clean and healthy food and how these habits can help him to gain profit for his business.

b. If a pani puriwalla is serving the pani puri with dirty hands, then we should not consume it. We sholud insist him to wash his hands and wear gloves while serving the pani puris.

c. If we have purchased large amounts of fruits and vegetables, then we need to store them properly. Some of the fruits can be used to make juices, jams and jellies which would increase their shelf life and also make it easy to store food. Vegetables can be cut and stored in deep freezers and then used as and when required. Some vegetables can also be used in making pickles.

d. Foodstuffs can be protected from rats, cockroaches etc. by storing them in proper conditions and proper areas. They should be stored in air tight containers and away from damp places which are the breeding places for these organisms.

Question 4:

Find the odd-man-out.
(a) salt, vinegar, citric acid, sodium benzoate
(b) lakhi dal, brick dust, metanyl yellow, turmeric powder
(c) banana, apple, guava, almond
(d) storing, freezing, settling, drying

ANSWER:

(a) salt, vinegar, citric acid, sodium benzoate- salt is the odd one out beacuse it is natural preservative while rest of them are chemical preservatives.

(b) lakhi dal, brick dust, metanyl yellow, turmeric powder - turmeric powder is the odd one out because it is a type of spice while the rest of the three are adulterants.

(c) banana, apple, guava, almond- almond is the odd one our because it is a dry fruit whereas the rest of the three are fresh fruits..

(d) storing, freezing, settling, drying- settling is the odd one out because rest of the three are preservation methods.
 

Question 5:

Complete the chart below.
 

S.No.	Foodstuff	Adulterant
1.	----------	Metanyl yellow
2.	Black pepper	----------
3.	----------	Iron filings
4.	Honey	----------

ANSWER:

S.No.	Foodstuff	Adulterant
1.	Turmeric powder	Metanyl yellow
2.	Black pepper	Papaya seeds
3.	Rava	Iron filings
4.	Honey	Sugar

Page No 40:

Question 6:

Explain why this happens and suggest possible remedies.
(a) Qualitative wastage of food.
(b) The cooked rice is underdone.
(c) The wheat that was bought is a bit moist.
(d) The taste of yoghurt is too sour/slightly bitter.
(e) Cut fruits have turned black.

ANSWER:

a. Wastage of food can either be qualitative or quantitative. Qualitative wastage of food is caused by:

• excessive use of preservatives
• over cooking of food
• washing vegetables after cutting them
• using wrong methods of protecting food
• mishandling of food products like fruits etc.

Qualitative wastage of food can be prevented by adopting steps like controlling the use of peservatives, taking care while cooking food to prevent it from being overcooked or undercooked, using proper methods of storage etc.

b. If the cooked rice is underdone, it can be used to make some foodstuff in which it can be reused. For example, underdone rice can be used to prepare kheer in which it can be cooked further with milk, or it can further be cooked to make papads or something else which would avoid its wastage.

c. If the wheat which was brought was little moist, it could be dried under the sun to remove this moisture. It is important to remove this moisture before grinding the wheat or storing it because it can act as a factor for the growth of microorganisms leading to its spoilage.

d. The taste of yoghurt could turn a little sour because it has undergone too much fermentation. The first thing would be to store this yoghurt in cold environment to stop further souring of the yoghurt. This yoghurt can then be used to make sweet lassi or some other delicacy like sindhi curry. 

e. Cut fruits turn black due to oxidation. Small amount of lemon juice should be applied to the surface of cut fruits as it prevents the oxidation of the fruits. 

Question 7:

Give reasons.
1. Food remains safe at 5° Celsius.
2. Nowadays, food is served buffet style during large gatherings.

ANSWER:

a. Food remains safe at 5^oC because this temperature prevents the growth of microorganisms. Microorganisms usually require hot and humid places to grow whereas at this temperature they cannot grow and survive. Their metabolic activities are inhibited at this temperature.

b. Nowadays, foods are served in buffet style during large gatherings to prevent the wastage of food. Every indivisual can choose what to eat and how much to eat according to their wish and thus prevents the wastage of food.

Credit:www.meritnation.com

Problem set No.14

Word Problems:

Problem set No.13

Q.1.The Forest Department planted 23,078 trees of khair,   19,476 of behada besides trees of several other kinds.

If the department planted 50,000 trees altogether, How many trees were neither of khair nor of behada?

Answer:

---------------------------------------------------

Answer:

No.of khair trees    :      2 3 0 7 8

No.of behada trees :      1 9 4 7 6

No.of khair & behada trees together

            2 3 0 7 8

       +   1 9 4 7 6    

            4 2 5 5 4

No.of khair & behada trees together = 42554

Forest Department planted 50,000 trees altogether out of which 23,078 trees are of khair and 19476 trees are of behada.

To find number of trees other than khair and behada.

Total No.of trees      :        5 0 0 0 0

No.Khair & behada   :        4 2 5 5 4

trees together 

                        5 0 0 0 0

                     -  4 2 5 5 4

                           7 4 4 6

Therefore,The number of trees other than khair and behada are 7446.

Let us verify our answer,

Total number plants 50000

Therefore,

No.of Khair plants     :     2 3 0 7 8

No.of Behada plants :     1 9 4 7 6

No.of other plants     :        7 4 4 6

Overall Total               :     5 0 0 0 0

Q.2

A city has a population of 37,04,926. If this includes 11,24,069 men and 10,96,478 women.

What is the number of children in the city?

Answer:

The population of a city including all

=37,04,926

Number of mens in the city: 11,24,069

Number of womens in the city:10,96,478

   1 1 2 4 0 6 9

+ 1 0 9 6 4 7 8

   2 2 2 0 5 4 7        (No.mens & womens 

                                                    together)

To find number of children in the city,

Let us subtract no. mens and womens from the Overall population of the city.

       3 7 0 4 9 2 6

    -  2 2 2 0 5 4 7

       1 4 8 4 3 7 9

Therefore, The number of childrens in the city = 14,84,379

Let us verify our answer

Population of the city: 37,04,926

            No.of males     :  1 1 2 4 0 6 9

            No.of females :   1 0 9 6 4 7 8 

      +    No.of children :   1 4 8 4 3 7 9

                                           3 7 0 4 9 2 6

Question No.3

Std.VII. Measurement of Physical Quantities

Question 1:

Write answers to the following questions in your own words.

(a) Why is the weight of the same object different on different planets?

(b) What precautions will you take to make accurate measurements in day-to-day affairs?

(c) What is the difference between mass and weight?

ANSWER:

(a) Weight of an object, W is given as

W=mgW=mg

where, m = mass of the object and g = acceleration due to gravity of a place

We know that acceleration due to gravity is different at different planets. Hence, the weight of same object differs on different planets.

(b) Precautions to be take to make accurate measurements in day-to-day affairs are

The device used for measurement should be appropriate and properly working.

The device should be used properly.

It should be checked that the device in use should have stamp of standardization by the department of weights and measure.

3-4 readings should be taken for achieving accuracy in measurement

C)

Question 2:

Who is my companion ?

Group 'A'               Group 'B'

(1) Velocity       (a) litre

(2) Area             (b) kilogram

(3) Volume        (c) metre/second

(4) Mass            (d) kilogram/cubic metre

(5) density         (e) square metre

ANSWER:

Group 'A'     Group 'B'

 (1) Velocity    (c) metre/second

(2) Area           (e) square metre

(3) Volume      (a) litre

(4) Mass          (b) kilogram

(5) Density       (d) kilogram/cubic metre

Question 3:

Explain giving examples.

(a) Scalar quantity

(b) Vector quantity

ANSWER:

(a) A quantity which has only magnitude and no direction is known as scalar quantity. Distance, work, speed, time, energy, etc. are all scalar quantities. These quantities can be expressed completely by their magnitude alone.

(b) A quantity which has magnitude as well as direction is known as vector quantity. Force, velocity, displacement, etc. are all vector quantities. These quantities are expressed completely only when their directions are defined along with their magnitude.

Question 4:Explain, giving examples, the errors that occur while making measurements.

ANSWER:

Various types of errors can occur while taking measurement. These are as follows:

Instrumental errors: These errors arise when the instrument used for measurement has become faulty. For eg, ruler with rough and broken edge can cause instrumental error.

Observational errors: These errors arise when the reading in the instrument is noted incorrectly. These can also arise if the instrument is used in incorrect method. For example, if the tip of pencil does not coincide with zero of the scale, then we will get error in measurement of length of pencil.

Theoretical errors: These are caused by simplification of the model system. For example, a theory states that the temperature of the system surrounding will not change the readings taken when it actually does, then this factor will begin a source of error in measurement.

Environmental errors: These errors arises due to the instruments working getting affected due to some environmental factors such as temperature, pressure, etc.

Question 5:

Give reasons.

(a) It is not proper to measure quantities by using body parts as units.

(b) It is necessary to get the weights and measures standardized at regular intervals.

ANSWER:

(a) It is not proper to measure quantities by using body parts as units because these are not reliable and unique. These units of measurement vary from person to person.

(b) Because of difference in physical conditions from place to place, the reference chosen as units for weights and measures varies. So, it becomes necessary to get the weights and measures standardized at regular intervals.

Question 6:Explain the need for accurate measurement and the devices to be used for that.

ANSWER:

We need not be very accurate every time we take a measurement. The degree of accuracy in measurements vary according to the situations. For example,

when someone asks about the time of the day, we do not have to be specific up to the seconds of time, because there is no need to be that accurate in the given situation. On the other hand, for laboratory purposes or for scientific experiments, we have to measure the time even up to milliseconds accurately.

while measuring mass of precious substances, such as gold, silver, etc., we need to be accurate in our measurement.

in competitions and events, a difference of second can make you lose or win the game. Thus, accurate time measurement in such cases is very important.

shopping in our day to day life, like for groceries, milk, flour etc. requires lot of alertness at our part so that we do not get cheated. We should always check whether the measurement is done properly or not by the vendors selling these products.

The devices used for accurate measurement are:

For time measurement, stop watch can be an accurate device

For mass measurement, electronic balance can be an accurate device.

For length measurement, ruler or measuring tape can be the accurate devices.

For temperature measurement, thermometers can be an accurate device

Credit: www.meritnation.com

For Class 1- 4 (Competitions organised by Nehru Science Centre)

(This message is from Nehru Science Centre, Mumbai)

Dear All,

Greetings...!!!

Nehru Science Centre, Mumbai is celebrating the Culmination of 150th Anniversary of Mahatma Gandhi. We have organized various competitions and lectures on this occasion. Please find the details of the program in the poster. 

The links for participation and details of various competitions are given in below links: 

 Fancy Dress Competition

 for class 1 to 4:

 https://tinyurl.com/oct2fancydress

Please note that the last date for participation for above events is September 27, 2020. 

The winners will be announced on October 9, 2020 on our Facebook page and website. 

Please note that the first 5 winners in all above competitions will get digital certificates. 

Please share this information with interested participants. 

---
Sheetal C. 

Thanks & Regards,

नेहरु विज्ञान केन्द्र    Nehru Science Centre
राष्ट्रीय विज्ञान संग्रहालय परिषद  (National Council of Science Museums)
संस्कृति मंत्रालय,  भारत सरकार Ministry of Culture, Government of India
वर्ली मुंबई  Worli Mumbai INDIA 400018

Look at the following pictures 

(Just for an awareness purpose)

Std.5 to 7 ( Essay Competition)

Dear Students,

Its an awesome opportunity to showcase your writing skills, understanding of the subject, comprehension, talent etc.

Please do participate in the competition organized by Nehru Science Centre.

Read the details given below.

Essay competition

for class 5 to 7

https://tinyurl.com/oct2essay5to7

Look at the following  screen shots

( just for an awareness purpose only)