Class: 7
Lesson objectives:
- Repetition and consolidation of previously acquired knowledge. Develop the ability to observe and analyze phenomena, answer questions briefly and logically.
- Educational: to promote the development in students of the ability to independently draw a conclusion, build a hypothesis and confirm it with experience.
- Educational: promote the development of the ability to work in a group, cooperate, listen to a friend, respect the opinion of an opponent; create conditions for the development of schoolchildren's desire for knowledge; the formation of a worldview idea of the knowability of phenomena and properties of the surrounding world.
- Developmental: create conditions for the development of speech skills in schoolchildren; promote the development of abilities for analysis and synthesis; promote the development of theoretical thinking.
Board design:
Date of. Lesson topic: Initiation to physics.
The purpose of the lesson: Systematize knowledge, develop the ability to observe and analyze phenomena, answer questions briefly and logically.
D/z: Make a crossword puzzle.
Drawings with errors.
Lesson type: combined.
Form: a lesson in the integrated application of knowledge.
Equipment: flask - 26 pcs., potassium permanganate, dynamometer - 16 pcs., weight (100g) - 26 pcs., a roll of parchment with the “Decree”, drawings with errors, poster “Task”, poster “Hockey Field”, kefir bottle, egg, glass of water, paper, matches, saucer, coin, paraffin ball.
During the classes
- Organizing time.
- Testing knowledge on the topic: molecular structure of matter.
- Testing knowledge on the topic: movement of bodies.
- Testing knowledge on the topic: density.
- Testing knowledge on the topic: strength.
- Homework.
- Lesson summary. Reflection.
Teacher: Hello, guys! Today in class we are starting to study a new and very interesting topic - “Pressure”.
Mr. Pressure: (enters the classroom, interrupting the teacher). Is this 7th grade? I have an order from Her Majesty Physics (reads).
"Order of Her Majesty Physics. Before studying a very important and complex topic“Pressure” I order: To punish ignoramuses in the most severe manner and, on the contrary, to initiate active and knowledgeable students into physics. Allow the study of the topic "Pressure" only if
if there is not a single know-nothing left in the class. To test your knowledge, invite Miss Molecule, Miss Density, Miss Strength. Appoint Mr. Pressure (i.e., me) as responsible for the execution of this order."
Now I will test all your knowledge. For this I invite my assistants. Well, Miss Molecule, let's start with you.
Miss Molecule: I can already see in my eyes that in this class there are only know-nothings. Well, tell me:
What is a molecule?
They say that molecules are motionless, is this true?
How do molecules interact with each other?
What is the difference between solids, liquids and gases?
What is diffusion?
How can you use a crystal of potassium permanganate to find out which of the two test tubes contains hot water?
(Children answer questions and complete a practical task.)
Miss Molecule: There are geniuses in this class. I take back what I said about his ignorance and count this topic. How do you know the topic of speed? IN Everyday life You encounter it all the time, so knowing it is essential.
What is speed?
Using the cards that are on the table, find the correct letter designation speed, path, time, unit of speed, unit of time, unit of path.
How are you able to solve problems? Let's check it now.
Problem about Baba Yaga: Baba Yaga flew in a mortar at a speed of 20 m/s for 5 minutes, then ran 2 km through the forest for half an hour, then swam across a pond 1000 m wide at a speed of 0.5 m/s. How fast did she chase poor Ivanushka?<Рисунок1>.
Given: SI: Solution: v 1 =20 m/s v av = S/t t 1 =5 min = 300 s S = S 1 + S 2 + S 3 S 2 =2 km = 2000 m t = t 1 + t 2 + t 3 t 2 =0.5 h = 1800 s S 1 = v 1 * t 1 S 3 =1000 m S 1 = 20 m/s * 300 s = 6000 m v 3 =0.5 m/s t 3 = S 3 / v 3 -------------- t 3 = 1000 m / 0.5 m/s = 2000 s v av - ? S = 6000 m + 2000 m + 1000 m = 9000 m t = 300 s + 1800 s + 2000 s = 4100 s v av = 9000 m / 4100 s = 2.195 m/s = 2.20 m/s Answer: v av = 2.20 m/s
I have to admit that they also know the concept of speed very well.
Mr. Pressure: Then I turn to Miss Density. Surely this is where they will get confused!
Miss Density: I will do this with great pleasure. Here are theoretical tasks for you:
What is density?
Using the cards on the table, find the correct density letter and density unit.
In front of you are several bodies of the same volume, but different masses. Could this be the case and why?
Find errors in the pictures.<Рисунок2>,<Рисунок3>,<Рисунок4>
Match the answer with the poster "Density"<Рисунок5>hanging on the wall.
Miss Density: I'm blown away by the knowledge of this class! They know everything about density!
Mr. Pressure: Then I call Miss Power, the strongest and most powerful, to help.
Miss Power: They definitely don’t know me. But if at least one doesn’t answer my question, I’ll crush him into a cake!
What is power?
Using the cards on the table, find the correct letter for force and unit of force.
What forces do you know, what are their differences and similarities?
What determines the result of a force? : And now we’ll check this by playing hockey<Рисунок6>. When you play sports, you apply different forces all the time. Every time you hit the puck, you apply force to it. The force you apply can cause the puck to start moving or, if it is already moving, to speed up, slow down, change direction, or stop. In what direction should a force be applied to the puck to stop puck No. 1 (to the left); Puck No. 2 (to the right) moved faster; Puck No. 3 (to the left) moved more slowly; puck No. 4 (down) hit the red goal; Puck No. 8 (down) moved more slowly; Puck No. 7 (down) moved faster; stop puck No. 6 (down); puck No. 5 (up) hit the blue goal.
Can you cope with the practical task: using a spring and a weight, predict the behavior of a weight suspended on a spring, having first made a drawing in a notebook indicating all the forces acting on it. One student does this work at the board.
(Children answer questions and complete the final practical task.)
Miss Power: Dear Mr. Pressure! Even I, so strong and brave, must admit defeat. They know the answers to all questions!
Mr. Pressure: Dear teacher! Your class showed excellent knowledge of physics. On behalf of Her Majesty the Physicist, I present you with the official certificates of "Initiation into Physics"<Рисунок7>and permission to study the topic "Pressure". And also, on behalf of Her Majesty Physics, to award grades to the most active students.
Teacher: I am very happy for the guys, they passed this test. This means that from the next lesson you will again learn a lot of new things about nature and its laws. Guys, what did you like most about the lesson? What would you like to know more about? When was it interesting and when was it boring? What were the difficulties? What surprised you? Are you satisfied with your work in class? Please write down today's homework in your diaries: create a crossword puzzle based on the material you have studied, so that the key word is: pressure.
(If there is time left) - Could you, dear Mr. Pressure, show us some interesting experiments, where you would play the lead role?
Mr. Pressure: I'll do it with great pleasure. (Shows experiments:
- "Persistent Egg": A hard-boiled and peeled egg will not fit into a milk bottle. Light a strip of paper, put it in the bottle and cover the bottle with an egg - it will fall.
- "Sticky Paper": pour into glass of water, cover with a sheet of paper and, supporting the sheet with your hand, turn the glass upside down. If you now take your hand away from the paper, the water will not spill out of the glass. The paper will remain glued to the edge of the glass. Why? Justify your answer.
- "Diving bell": lower a paraffin ball to the bottom of a large glass vessel. Place a glass (the diameter of which is 2-3 times larger than the diameter of the ball) upside down in this vessel and cover the ball with it. Raise the glass up and the ball will rise with it. When the ball floats on the surface of the water, carefully remove the glass. The paraffin ball can be replaced with a cork circle with a piece of sugar on it. Then the cork piece should be on the surface of the water.
- “Dry from the water”: place a coin on a flat plate and pour water. Light the paper inside the glass and, when the air heats up, tip the glass onto a plate next to the coin. When the water is drawn into the glass, you can pick up the coin without getting your fingers wet.
Application.
Problem about Baba Yaga: Baba Yaga flew in a mortar at a speed of 20 m/s for 5 minutes, then ran 2 km through the forest for half an hour, then swam across a pond 1000 m wide at a speed of 0.5 m/s. How fast did she chase poor Ivanushka?
Class: 7
Lesson objectives:
- Repetition and consolidation of previously acquired knowledge. Develop the ability to observe and analyze phenomena, answer questions briefly and logically.
- Educational: to promote the development in students of the ability to independently draw a conclusion, build a hypothesis and confirm it with experience.
- Educational: promote the development of the ability to work in a group, cooperate, listen to a friend, respect the opinion of an opponent; create conditions for the development of schoolchildren's desire for knowledge; the formation of a worldview idea of the knowability of phenomena and properties of the surrounding world.
- Developmental: create conditions for the development of speech skills in schoolchildren; promote the development of abilities for analysis and synthesis; promote the development of theoretical thinking.
Board design:
Date of. Lesson topic: Initiation to physics.
The purpose of the lesson: Systematize knowledge, develop the ability to observe and analyze phenomena, answer questions briefly and logically.
D/z: Make a crossword puzzle.
Drawings with errors.
Lesson type: combined.
Form: a lesson in the integrated application of knowledge.
Equipment: flask - 26 pcs., potassium permanganate, dynamometer - 16 pcs., weight (100g) - 26 pcs., a roll of parchment with the “Decree”, drawings with errors, poster “Task”, poster “Hockey Field”, kefir bottle, egg, glass of water, paper, matches, saucer, coin, paraffin ball.
During the classes
- Organizing time.
- Testing knowledge on the topic: molecular structure of matter.
- Testing knowledge on the topic: movement of bodies.
- Testing knowledge on the topic: density.
- Testing knowledge on the topic: strength.
- Homework.
- Lesson summary. Reflection.
Teacher: Hello, guys! Today in class we are starting to study a new and very interesting topic - “Pressure”.
Mr. Pressure: (enters the classroom, interrupting the teacher). Is this 7th grade? I have an order from Her Majesty Physics (reads).
"Order of Her Majesty Physics. Before studying the very important and complex topic "Pressure", I order: To punish ignorant people in the most strict way and, on the contrary, to initiate active and knowledgeable students into physics. Allow the study of the topic "Pressure" only in that
if there is not a single know-nothing left in the class. To test your knowledge, invite Miss Molecule, Miss Density, Miss Strength. Appoint Mr. Pressure (i.e., me) as responsible for the execution of this order."
Now I will test all your knowledge. For this I invite my assistants. Well, Miss Molecule, let's start with you.
Miss Molecule: I can already see in my eyes that in this class there are only know-nothings. Well, tell me:
What is a molecule?
They say that molecules are motionless, is this true?
How do molecules interact with each other?
What is the difference between solids, liquids and gases?
What is diffusion?
How can you use a crystal of potassium permanganate to find out which of the two test tubes contains hot water?
(Children answer questions and complete a practical task.)
Miss Molecule: There are geniuses in this class. I take back what I said about his ignorance and count this topic. How do you know the topic of speed? In everyday life you come across it all the time, so knowing it is simply necessary.
What is speed?
Using the cards on the table, find the correct letter for speed, path, time, unit of speed, unit of time, unit of path.
How are you able to solve problems? Let's check it now.
Problem about Baba Yaga: Baba Yaga flew in a mortar at a speed of 20 m/s for 5 minutes, then ran 2 km through the forest for half an hour, then swam across a pond 1000 m wide at a speed of 0.5 m/s. How fast did she chase poor Ivanushka?<Рисунок1>.
Given: SI: Solution: v 1 =20 m/s v av = S/t t 1 =5 min = 300 s S = S 1 + S 2 + S 3 S 2 =2 km = 2000 m t = t 1 + t 2 + t 3 t 2 =0.5 h = 1800 s S 1 = v 1 * t 1 S 3 =1000 m S 1 = 20 m/s * 300 s = 6000 m v 3 =0.5 m/s t 3 = S 3 / v 3 -------------- t 3 = 1000 m / 0.5 m/s = 2000 s v av - ? S = 6000 m + 2000 m + 1000 m = 9000 m t = 300 s + 1800 s + 2000 s = 4100 s v av = 9000 m / 4100 s = 2.195 m/s = 2.20 m/s Answer: v av = 2.20 m/s
I have to admit that they also know the concept of speed very well.
Mr. Pressure: Then I turn to Miss Density. Surely this is where they will get confused!
Miss Density: I will do this with great pleasure. Here are theoretical tasks for you:
What is density?
Using the cards on the table, find the correct density letter and density unit.
In front of you are several bodies of the same volume, but different masses. Could this be the case and why?
Find errors in the pictures.<Рисунок2>,<Рисунок3>,<Рисунок4>
Match the answer with the poster "Density"<Рисунок5>hanging on the wall.
Miss Density: I'm blown away by the knowledge of this class! They know everything about density!
Mr. Pressure: Then I call Miss Power, the strongest and most powerful, to help.
Miss Power: They definitely don’t know me. But if at least one doesn’t answer my question, I’ll crush him into a cake!
What is power?
Using the cards on the table, find the correct letter for force and unit of force.
What forces do you know, what are their differences and similarities?
What determines the result of a force? : And now we’ll check this by playing hockey<Рисунок6>. When you play sports, you apply different forces all the time. Every time you hit the puck, you apply force to it. The force you apply can cause the puck to start moving or, if it is already moving, to speed up, slow down, change direction, or stop. In what direction should a force be applied to the puck to stop puck No. 1 (to the left); Puck No. 2 (to the right) moved faster; Puck No. 3 (to the left) moved more slowly; puck No. 4 (down) hit the red goal; Puck No. 8 (down) moved more slowly; Puck No. 7 (down) moved faster; stop puck No. 6 (down); puck No. 5 (up) hit the blue goal.
Can you cope with the practical task: using a spring and a weight, predict the behavior of a weight suspended on a spring, having first made a drawing in a notebook indicating all the forces acting on it. One student does this work at the board.
(Children answer questions and complete the final practical task.)
Miss Power: Dear Mr. Pressure! Even I, so strong and brave, must admit defeat. They know the answers to all questions!
Mr. Pressure: Dear teacher! Your class showed excellent knowledge of physics. On behalf of Her Majesty the Physicist, I present you with the official certificates of "Initiation into Physics"<Рисунок7>and permission to study the topic "Pressure". And also, on behalf of Her Majesty Physics, to award grades to the most active students.
Teacher: I am very happy for the guys, they passed this test. This means that from the next lesson you will again learn a lot of new things about nature and its laws. Guys, what did you like most about the lesson? What would you like to know more about? When was it interesting and when was it boring? What were the difficulties? What surprised you? Are you satisfied with your work in class? Please write down today's homework in your diaries: create a crossword puzzle based on the material you have studied, so that the key word is: pressure.
(If there is time left) - Could you, dear Mr. Pressure, show us some interesting experiments where you would play a leading role?
Mr. Pressure: I'll do it with great pleasure. (Shows experiments:
- "Persistent Egg": A hard-boiled and peeled egg will not fit into a milk bottle. Light a strip of paper, put it in the bottle and cover the bottle with an egg - it will fall.
- "Sticky paper": pour water into a glass, cover it with a sheet of paper and, supporting the sheet with your hand, turn the glass upside down. If you now take your hand away from the paper, the water will not spill out of the glass. The paper will remain glued to the edge of the glass. Why? Justify your answer.
- "Diving bell": Place a paraffin ball at the bottom of a large glass vessel. Place a glass (the diameter of which is 2-3 times larger than the diameter of the ball) upside down in this vessel and cover the ball with it. Raise the glass up and the ball will rise with it. When the ball floats on the surface of the water, carefully remove the glass. The paraffin ball can be replaced with a cork circle with a piece of sugar on it. Then the cork piece should be on the surface of the water.
- “Dry from the water”: place a coin on a flat plate and pour water. Light the paper inside the glass and, when the air heats up, tip the glass onto a plate next to the coin. When the water is drawn into the glass, you can pick up the coin without getting your fingers wet.
Application.
Problem about Baba Yaga: Baba Yaga flew in a mortar at a speed of 20 m/s for 5 minutes, then ran 2 km through the forest for half an hour, then swam across a pond 1000 m wide at a speed of 0.5 m/s. How fast did she chase poor Ivanushka?
Funny non-standard problems in physics 7th grade.
To consolidate the concept of average speed as a relationship all the way to everything The time spent on this path can be given a number of fun non-standard problems that are solved by students with great interest.
1 Baba Yaga flew in a mortar at a speed 20 m/s for 5 min , then ran for half an hour 2 km through the forest, then swam across a pond wide 1000m at a speed of 0.5 m/s. At what average speed did she chase poor Ivanushka? (Answer: 2.2 m/s)
2. The hedgehog rolled down a slope as long as 10 m at a speed of 20 cm/s , then opened up and ran some more 30 m in 1 min. At what average speed did the hedgehog move? (Answer: 0.36m/s)
3. The ant climbs up 10 meter birch with speed 1 cm/s. What is it average speed if in the middle of the way he did 5 minute stop? (Answer: 0.0077 m/s)
4. A fly sat on the edge of a record with a diameter of 20 cm. rotating with frequency33 rpmand rides with the breeze. What is the average speed of this breeze? (Answer: 0.36 m/s).
Attention: the source data is presented in a variety of units; they must be converted to the SI system.
Challenges for ingenuity.
- The athlete pilot managed to land the plane on the roof passenger car. At what physical condition is this possible?
- The train passes the observer within 10 s, and across a bridge 400 m long - within 30 s. Determine the length of the train. (Answer: 200m, 20 m/s).
Municipal budgetary institution
Bazkovskaya secondary school
Art. Bazkovskaya, Sholokhovsky district, Rostov region
Methodological development
Entertaining tasks for physics lessons in 9th grade
Prepared by: physics teacher
Biryulina Natalya Ivanovna
st.Bazkovskaya
9th grade. Oscillations and waves. Sound/
Option 1.
1.When I, the famous Baron Munchausen, once again went to the Moon, I took my favorite watch with me. So what would you think? The clock on the Moon is not running correctly! Answer, is a pendulum clock on the Moon slow or fast? Why?
2. Once I went to the sea to fish. Sitting in a boat with a fishing rod, I discovered that the float rose on the wave every 8 seconds. The distance between the wave crests turned out to be 24 m. Determine what the speed of the waves is? Can I use a wave to travel as fast as it travels without oars or a sail?
3. Being carried away by fishing, I did not notice how the boat broke from its anchor and was carried away by the wind and mysterious sea currents far from the shore. But then in the distance I saw a steamer. Approaching closer, the steamer sounded its whistle (I saw puffs of steam), which I heard after 3 seconds. After 3.4 minutes, I was already being lifted on board. I, a person well acquainted with technology, was interested in the steamer, and I wanted to ask the sailors about its speed, but I immediately calculated it myself, knowing the speed of sound in air - 340 m/s. Can you find the speed of the ship?
4. The sea was calm, the barometer showed “Clear”, I talked on deck with the famous Doctor Gulliver, who was returning from one of his amazing journeys. Suddenly the ship's cat began to scamper around the deck, fish jumped out of the water, and we began to experience vague anxiety. Gulliver suggested that an underground earthquake occurred somewhere and infrasonic waves arose. What are these waves and why do they have such a strange effect on people?
Option – 2
1. Baba Yaga went to the mountains to ski in winter and took a cuckoo clock with her. How did she have to change the length of the pendulum to keep the clock accurate, and why?
2. On the way from the ski resort, Baba Yaga decided to look at Koshchei the Immortal. Flying up to his castle, she almost collided with the Serpent Gorynych. Fortunately for Baba Yaga, Gorynych is a heavy smoker, so he periodically spews flames from all his mouths and coughs irritably. Yaga saw the flame, and 2 s later she heard the cough accompanying it and managed, by turning the mortar, to avoid a collision that would have occurred 34 s after she saw the flash. Determine at what speed (in km/h) the Serpent Gorynych flies.
3. Sipping from an elegant cup living water, Serpent Gorynych complained to his interlocutors that after the next duel with Ivan the Tsarevich, the frequency of the flapping of his wings decreased and is now 0.5 Hz. What is the period of oscillation of the wings of the Serpent Gorynych? How many swings does he make in 10 s?
4. A huge number of bats are constantly circling around the towers of the castle of Koshchei the Immortal. The guests were surprised how these animals navigate, why in the dark they do not constantly bump into towers, ledges and other architectural decorations, because the castle is known for its splendor far beyond the borders of the Far Away Kingdom. Koschey explained that mice navigate using ultrasound and people also use it to determine distances. What is ultrasound and how do mice, and following their example, people use it?
Solutions and Answers
Option 1
1. Since the acceleration of gravity on the Moon is less, the period of oscillation of the pendulum T = 2 l / g increases and the clock lags behind.
2. v = /T = 3m/s; the wave does not transport matter.
3. v = t *v /t =(3 s*340 m/s)/(3.4*60 s) = 5 m/s =18 km/h.
4. Infrasonic vibrations have frequencies lower than sound ones. When they coincide with the natural frequencies of oscillations internal organs resonance occurs, which causes unpleasant sensations.
Option – 2
1. The length of the pendulum needs to be reduced, because acceleration of free fall by high altitude less.
2. v = t *v /t = (2 s*340 m/s)/(34 s) = 20 m/s = 72 km/h.
3. T =1/v = 2c ;n = t *v =5
4. Ultrasonic vibrations have frequencies higher than sound ones, the bats receive information about obstacles by emitting an ultrasonic pulse and perceiving an echo signal. An echo sounder is designed on this principle.
Entertaining problems on the topic “mechanical vibrations”, grade 9.
Tasks
1. Two monkeys swing on the vines, flying past the palm tree 19 times, and the other 21 times. What is the length of the vines if one is 1 m longer than the other?
2. A boy carries a bucket of water on a rocker; the period of natural oscillations is 1.6 s. At what speed will the water begin to splash out especially strongly if the boy’s stride length is 60 cm?
3. To demolish buildings, a truck crane is used, on the boom of which a 10 m long cable with a massive load is suspended. The crane can impart a maximum speed of 4 m/s to the load. Is it worth sending such a crane to break a wall if it is known that it can be approached at a distance of up to 3 m, and the speed of the load before impact must be at least 2 m/s?
4. A toy is suspended in the car by a spring. The driver stops abruptly at the traffic light so that the toy begins to swing up and down and, at the greatest deviation downwards by 5 cm, obscures the traffic light from the driver. How many times will the toy block the traffic light if the car sits for 15 seconds? Maximum speed toys 15 m/s.
5. To estimate the density of lunar soil, the astronaut tightly filled a capsule with a mass of 5 g and a volume of 10 cm³ and suspended it from a spring with a stiffness of 1 N/m. The period of capsule oscillation turned out to be 1.2 s. What is the density of soil?
6. A monkey swings on a 4.5 m long vine so that it flies past banana tree. Flying every fourth time, she picks a banana. How many bananas will she eat if she rocks for 2 minutes?
7. The machine experiences vibrations during operation due to the displacement of the center of mass of the engine rotor relative to the axis of rotation. Is there a danger of destruction of the support on which the machine is installed at an engine speed of 3·10³ sˉ¹, if the rigidity coefficient of the support is 1.5·10¹² N/m, its mass is 500 kg, and the mass of the machine is 100 kg?
2.Physics. 7-9 grades. Collection of problems in physics. V. I. Lukashik, E. V. Ivanova:
Speed in mechanical movement
Entertaining tasks.
Baba Yaga flew in a mortar at a speed of 20 m/s for 5 minutes, then ran 2 km through the forest for half an hour, then swam across a pond 1000 m wide at a speed of 0.5 m/s. At what average speed did she chase poor Ivanushka? (Answer: 2.2m/s)
A hedgehog rolled down a slope 10 m long at a speed of 20 cm/s, then opened up and ran another 30 m in 1 minute. At what average speed did the hedgehog move? (Answer: 0.36m/s)
An ant climbs up a 10-meter birch tree at a speed of 1 cm/s. What is his average speed if he stops for 5 minutes in the middle of the journey? (Answer: 0.0077m/s)
The fly sat on the edge of a gramophone record with a diameter of 20 cm, rotating at a frequency of 33 revolutions per minute, and rolled around “with the breeze.” What is the average speed of this breeze? (Answer: 0.36m/s)
An ostrich runs at a speed of 22m/s. How far did he cover in 1 minute? (Answer: 1320m)
The turtle crawled 5m. How long did her journey take if her speed was 0.1 m/s? (Answer: 50s)
The speed of a hare is 15 m/s, and the speed of a dolphin is 18 km/h. Which one is faster?
The speed of a diesel locomotive is 28 m/s, and that of a car is 36 km/h. Which one is faster?
The speed of the electric locomotive is 25 m/s, and the speed of the Moskvich car is 108 km/h. Which one is faster?
The starling's speed is 72 km/h, and the cyclist's speed is 25 m/s. Which one is faster?
Misha runs at a speed of 18 km/h after Sasha, who is running away from him at a speed of 12 m/s. Will Misha catch up with Sasha?
A group of tourists, moving in a chain along the side of the road at a speed of 3.6 km/h, stretched for 200 m. The leader sends the cyclist to the leader walking ahead of the group. The cyclist rides at a speed of 7 m/s, having completed the assignment, he immediately returns to the leader of the group at the same speed. How long after receiving the task did the cyclist return?
