Альпинист массой m = 80 кг спускается с отвесной скалы, скользя по вертикальной веревке с ускорением a = 0,4 м/с2, направленным вниз. Пренебрегая массой веревки, определите силу T ее натяжения.
Решение
Согласно третьему закону Ньютона альпинист действует на веревку с такой же по модулю силой, с какой веревка действует на альпиниста. На альпиниста действуют две силы: сила тяжести  направленная вертикально вниз, и упругая сила  веревки, направленная вверх. По второму закону Ньютона
ma = mg – T.
Следовательно, сила натяжения веревки T равна
T = m(g – a) = 752 Н.
Если бы альпинист спускался по веревке с постоянной скоростью или неподвижно висел на ней, то сила T' натяжения была бы равна
Leonard James is a homeless man. For him, life is always hard. He is always hungry. His shoes have holes in them. He needs a haircut. His clothes are old and dirty. “What I would do with one hundred dollars!” Leonard says. This is a game he likes to play with himself to take his mind off things. He is walking down the street on a Thursday night. The winter air is cold on his face. “If I had one hundred dollars, I could buy new socks,” he says. He continues to walk down the street. “If I had one hundred dollars, I could get a haircut,” he says. He continues to walk down the street. “If I had one hundred dollars, I could buy new pants,” he says. He continues to walk down the street. “If I had one hundred dollars, I could get a hamburger,” he says. His stomach rumbles at the thought. “If I had….” Leonard looks down at the sidewalk. He cannot believe what he sees! Someone has lost his wallet. Leonard picks it up. Inside are five twenty-dollar bills. “One hundred dollars!” Leonard says. He is very excited. “Now I can buy everything I want!” Then Leonard begins to think. “But this is not my money,” he says. Leonard goes to the police station. He gives a police officer the wallet and money. “Thank you,” says the police officer. “You are a very honest man.” Leonard smiles. He turns around and begins to leave the police station. “Hold on,” the police officer says. He reaches in his own pocket and gives Leonard ten dollars. “Get yourself something to eat.”
Questions:
1) What is life like for Leonard?
A. It is hard.
B. It is easy.
C. It is warm.
D. It is full of good food.
2) How does the reader know that Leonard is poor? I. He finds a wallet. II. He has no home. III. He is always hungry.
A. I only
B. I and II
C. II and III
D. I, II, and III
3) Why does Leonard think about what he would do with a hundred dollars?
A. It helps him go to sleep.
B. It takes his mind off things.
C. The police officer asks him to.
D. He knows he will find the money.
4) What time of year is it?
A. spring
B. summer
C. fall
D. winter
5) What does Leonard say he would do with a hundred dollars? I. get a haircut II. buy new clothes III. get a hotel room
A. I only
B. I and II
C. II and III
D. I, II, and III
6) Why does Leonard's stomach rumble?
A. because he is hungry
B. because he is tired
C. because his clothes are dirty
D. because he is homeless
7) “He cannot believe what he sees.” What is another way to write this sentence?
A. He thinks what he sees is crazy.
B. He feels what he sees is good luck.
C. He thinks what he sees cannot be true.
D. He thinks what he sees is scary.
8) Why does Leonard go to the police station?
A. because he owes money
B. because he wants a reward
C. because the wallet is not his
D. because he has committed a crime
Questions (continued):
9) What kind of man does Leonard seem to be?
A. bad
B. dumb
C. good
D. old
10) As used at the end of the story, what does it mean to be honest?
A. to feel good
B. to want more
C. to be truthful
D. to be hopeful
11) How does Leonard seem to feel about what he has done?
A. angry
B. happy
C. sad
D. unsure
12) What does the police officer give Leonard?
A. advice
B. a handshake
C. money to eat
D. the one hundred dollars
13) What kind of man does the police officer seem to be?
A. angry
B. busy
C. kind
D. mean
14) Why does the police officer give Leonard ten dollars?
A. to surprise Leonard
B. so Leonard feels better about returning the wallet
C. because it is part of his job
D. because he wants to get Leonard off the streetsВітаємо в буфері обміну Gboard. Скопійований текст зберігатиметься тут.
Объяснение:
Альпинист массой m = 80 кг спускается с отвесной скалы, скользя по вертикальной веревке с ускорением a = 0,4 м/с2, направленным вниз. Пренебрегая массой веревки, определите силу T ее натяжения.
Решение
Согласно третьему закону Ньютона альпинист действует на веревку с такой же по модулю силой, с какой веревка действует на альпиниста. На альпиниста действуют две силы: сила тяжести  направленная вертикально вниз, и упругая сила  веревки, направленная вверх. По второму закону Ньютона
ma = mg – T.
Следовательно, сила натяжения веревки T равна
T = m(g – a) = 752 Н.
Если бы альпинист спускался по веревке с постоянной скоростью или неподвижно висел на ней, то сила T' натяжения была бы равна
T' = mg = 784 Н.
7 form Reading Test
One Hundred Dollars”
Read the story. Then answer the questions below.
Leonard James is a homeless man. For him, life is always hard. He is always hungry. His shoes have holes in them. He needs a haircut. His clothes are old and dirty. “What I would do with one hundred dollars!” Leonard says. This is a game he likes to play with himself to take his mind off things. He is walking down the street on a Thursday night. The winter air is cold on his face. “If I had one hundred dollars, I could buy new socks,” he says. He continues to walk down the street. “If I had one hundred dollars, I could get a haircut,” he says. He continues to walk down the street. “If I had one hundred dollars, I could buy new pants,” he says. He continues to walk down the street. “If I had one hundred dollars, I could get a hamburger,” he says. His stomach rumbles at the thought. “If I had….” Leonard looks down at the sidewalk. He cannot believe what he sees! Someone has lost his wallet. Leonard picks it up. Inside are five twenty-dollar bills. “One hundred dollars!” Leonard says. He is very excited. “Now I can buy everything I want!” Then Leonard begins to think. “But this is not my money,” he says. Leonard goes to the police station. He gives a police officer the wallet and money. “Thank you,” says the police officer. “You are a very honest man.” Leonard smiles. He turns around and begins to leave the police station. “Hold on,” the police officer says. He reaches in his own pocket and gives Leonard ten dollars. “Get yourself something to eat.”
Questions:
1) What is life like for Leonard?
A. It is hard.
B. It is easy.
C. It is warm.
D. It is full of good food.
2) How does the reader know that Leonard is poor? I. He finds a wallet. II. He has no home. III. He is always hungry.
A. I only
B. I and II
C. II and III
D. I, II, and III
3) Why does Leonard think about what he would do with a hundred dollars?
A. It helps him go to sleep.
B. It takes his mind off things.
C. The police officer asks him to.
D. He knows he will find the money.
4) What time of year is it?
A. spring
B. summer
C. fall
D. winter
5) What does Leonard say he would do with a hundred dollars? I. get a haircut II. buy new clothes III. get a hotel room
A. I only
B. I and II
C. II and III
D. I, II, and III
6) Why does Leonard's stomach rumble?
A. because he is hungry
B. because he is tired
C. because his clothes are dirty
D. because he is homeless
7) “He cannot believe what he sees.” What is another way to write this sentence?
A. He thinks what he sees is crazy.
B. He feels what he sees is good luck.
C. He thinks what he sees cannot be true.
D. He thinks what he sees is scary.
8) Why does Leonard go to the police station?
A. because he owes money
B. because he wants a reward
C. because the wallet is not his
D. because he has committed a crime
Questions (continued):
9) What kind of man does Leonard seem to be?
A. bad
B. dumb
C. good
D. old
10) As used at the end of the story, what does it mean to be honest?
A. to feel good
B. to want more
C. to be truthful
D. to be hopeful
11) How does Leonard seem to feel about what he has done?
A. angry
B. happy
C. sad
D. unsure
12) What does the police officer give Leonard?
A. advice
B. a handshake
C. money to eat
D. the one hundred dollars
13) What kind of man does the police officer seem to be?
A. angry
B. busy
C. kind
D. mean
14) Why does the police officer give Leonard ten dollars?
A. to surprise Leonard
B. so Leonard feels better about returning the wallet
C. because it is part of his job
D. because he wants to get Leonard off the streetsВітаємо в буфері обміну Gboard. Скопійований текст зберігатиметься тут.