Phương trình có bao nhiêu nghiệm?

Một vật dao động cưỡng bức với phương trình do tác dụng của ngoại lực tuần hoàn theo phương Ox có phương trình . Công của ngoại lực tuần hoàn tác dụng lên vật trong một chu kì có giá trị:

Read the following passage and mark the letter A, B, C or D to indicate the correct answer to each of the questions:

Many of the most damaging and life-threaling types of weather-torrential rains, severe thunderstorms, and tornadoes-begin quickly, strike suddenly, and dissipate rapidly, devastating small regions while leaving neighboring areas untouched. One such event, a tornado, struck the northeastern section of Edmonton, Alberta, in July 1987. Total damages from the tornado exceeded $250 million, the highest ever for any Canadian storm. Conventional computer models of the atmosphere have limited value in predicting short-live local storms like the Edmonton tornado, because the available weather data are generally not detailed enough to allow computers to discern the subtle atmospheric changes that precede these storms. In most nations, for example, weather balloon observations are taken just once every twelve hours at locations typically separated by hundreds of miles. With such limited data, conventional forecasting models do a much better job predicting general weather conditions over large regions than they do forecasting specific local events. Until recently, the observation-intensive approach needed for accurate, very short range forecasts, or “Nowcasts”, was not feasible. The cost of equipping and operating many thousands of conventional weather stations was prohibitively high, and the difficulties involved in rapidly collecting and processing the raw weather data from such a network were insurmountable. Fortunately, scientific and technological advances have overcome most of these problems. Radar systems, automated weather instruments, and satellites are all capable of making detailed, nearly continuous observation over large regions at a relatively low cost. Communications satellites can transmit data around the world cheaply and instantaneously, and modern computers can quickly compile and analyzing this large volume of weather information. Meteorologists and computer scientists now work together to design computer programs and video equipment capable of transforming raw weather data into words, symbols, and vivid graphic displays that forecasters can interpret easily and quickly. As meteorologists have begun using these new technologies in weather forecasting offices, Nowcasting is becoming a reality.  

Question: Which of the following is NOT mentioned as an advance in short-range weather forecasting?         

Khi nói về dao động cưỡng bức, phát biểu nào sau đây sai:         

Read the following passage and mark the letter A, B, C or D to indicate the correct answer to each of the questions:

Many of the most damaging and life-threaling types of weather-torrential rains, severe thunderstorms, and tornadoes-begin quickly, strike suddenly, and dissipate rapidly, devastating small regions while leaving neighboring areas untouched. One such event, a tornado, struck the northeastern section of Edmonton, Alberta, in July 1987. Total damages from the tornado exceeded $250 million, the highest ever for any Canadian storm. Conventional computer models of the atmosphere have limited value in predicting short-live local storms like the Edmonton tornado, because the available weather data are generally not detailed enough to allow computers to discern the subtle atmospheric changes that precede these storms. In most nations, for example, weather balloon observations are taken just once every twelve hours at locations typically separated by hundreds of miles. With such limited data, conventional forecasting models do a much better job predicting general weather conditions over large regions than they do forecasting specific local events. Until recently, the observation-intensive approach needed for accurate, very short range forecasts, or “Nowcasts”, was not feasible. The cost of equipping and operating many thousands of conventional weather stations was prohibitively high, and the difficulties involved in rapidly collecting and processing the raw weather data from such a network were insurmountable. Fortunately, scientific and technological advances have overcome most of these problems. Radar systems, automated weather instruments, and satellites are all capable of making detailed, nearly continuous observation over large regions at a relatively low cost. Communications satellites can transmit data around the world cheaply and instantaneously, and modern computers can quickly compile and analyzing this large volume of weather information. Meteorologists and computer scientists now work together to design computer programs and video equipment capable of transforming raw weather data into words, symbols, and vivid graphic displays that forecasters can interpret easily and quickly. As meteorologists have begun using these new technologies in weather forecasting offices, Nowcasting is becoming a reality.  

Question: With which of the following statements is the author most likely to agree?         

Một vật nhỏ có khối lượng 100g dao động theo phương trình (x tính bằng cm, t tính bằng s). Động năng cực đại của vật bằng:        

Read the following passage and mark the letter A, B, C or D on your answer sheet to indicate the correct answer ti each of the questions:

The issue of equality for women in British society first attracted national attention in the early 20th century, when the suffragettes won for women the right to vote. In the 1960s feminism became the subject of intense debate when the women’s liberation movement encouraged women to reject their traditional supporting role and to demand equal status and equal rights with men in areas such as employment and pay. Since then, the gender gap between the sexes has been reduced. The Equal Pay Act of 1970, for instance, made it illegal for women to be paid less than men for doing the same work, and in 1975 the Sex Discrimination Act aimed to prevent either sex having an unfair advantage when applying for jobs. In the same year the Equal Opportunities Commission was set up to help people claim their rights to equal treatment and to publish research and statistics to show where improvements in opportunities for women need to be made. Women now have much better employment opportunities, though they still tend to get less well-paid jobs than men, and very few are appointed to top jobs in industry. In the US the movement that is often called the “first wave of feminism” began in the mid 1800s. Susan B. Anthony worked for the right to vote, Margaret Sanger wanted to provide women with the means of contraception so that they could decide whether or not to have children, and Elizabeth Blackwell, who had to fight for the chance to become a doctor, wanted women to have greater opportunities to study. Many feminists were interested in other social issues. The second wave of feminism began in the 1960s. Women like Betty Friedan and Gloria Steinem became associated with the fight to get equal rights and opportunities for women under the law. An important issue was the Equal Rights Amendment (ERA), which was intended to change the Constitution. Although the ERA was not passed, there was progress in other areas. It became illegal for employers, schools, clubs, etc. to discriminate against women. But women still find it hard to advance beyond a certain point in their careers, the so-called glass ceiling that prevents them from having high-level jobs. Many women also face the problem of the second shift, i.e. the household chores. In the 1980s, feminism became less popular in the US and there was less interest in solving the remaining problems, such as the fact that most women still earn much less than men. Although there is still discrimination, the principle that it should not exist is widely accepted.  

Question: The phrase “glass ceiling” in paragraph 4 mostly means ______.         

Từ vị trí đứng yên cân bằng, truyền cho vật nhỏ của một con lắc đơn một vận tốc 157 (cm/s) theo phương ngang thì thấy con lắc dao động với biên độ góc 0,52 (rad). Biết gia tốc rơi tự do là 9,8 (m/s²). Bỏ qua mọi lực cản. Dây treo con lắc có chiều dài bằng:

Read the following passage and mark the letter A, B, C or D on your answer sheet to indicate the correct answer ti each of the questions:

The issue of equality for women in British society first attracted national attention in the early 20th century, when the suffragettes won for women the right to vote. In the 1960s feminism became the subject of intense debate when the women’s liberation movement encouraged women to reject their traditional supporting role and to demand equal status and equal rights with men in areas such as employment and pay. Since then, the gender gap between the sexes has been reduced. The Equal Pay Act of 1970, for instance, made it illegal for women to be paid less than men for doing the same work, and in 1975 the Sex Discrimination Act aimed to prevent either sex having an unfair advantage when applying for jobs. In the same year the Equal Opportunities Commission was set up to help people claim their rights to equal treatment and to publish research and statistics to show where improvements in opportunities for women need to be made. Women now have much better employment opportunities, though they still tend to get less well-paid jobs than men, and very few are appointed to top jobs in industry. In the US the movement that is often called the “first wave of feminism” began in the mid 1800s. Susan B. Anthony worked for the right to vote, Margaret Sanger wanted to provide women with the means of contraception so that they could decide whether or not to have children, and Elizabeth Blackwell, who had to fight for the chance to become a doctor, wanted women to have greater opportunities to study. Many feminists were interested in other social issues. The second wave of feminism began in the 1960s. Women like Betty Friedan and Gloria Steinem became associated with the fight to get equal rights and opportunities for women under the law. An important issue was the Equal Rights Amendment (ERA), which was intended to change the Constitution. Although the ERA was not passed, there was progress in other areas. It became illegal for employers, schools, clubs, etc. to discriminate against women. But women still find it hard to advance beyond a certain point in their careers, the so-called glass ceiling that prevents them from having high-level jobs. Many women also face the problem of the second shift, i.e. the household chores. In the 1980s, feminism became less popular in the US and there was less interest in solving the remaining problems, such as the fact that most women still earn much less than men. Although there is still discrimination, the principle that it should not exist is widely accepted.

Question: Which of the following is true according to the passage?         

Một hệ dao động chịu tác dụng của ngoại lực tuần hoàn thì xảy ra hiện tượng cộng hưởng, tần số dao động riêng của hệ phải là:

Khi một vật dao động cưỡng bức thì: