Con lắc lò xo gồm vật nhỏ và lò xo nhẹ có độ cứng 100N/m, dao động điều hòa trên mặt phẳng ngang dọc trục Ox. Gọi A,B và C nằm lần lượt trên trục Ox và theo chiều dương , biết AB= 5cm và BC=8,66 cm . Khi vật đi từ A đến B thì động năng của vật tăng thêm 25% (của động năng khi đến B) Vật đi từ B đến C thì tốc độ giảm đi một nửa . Mốc thế năng tại vị trí cân bằng của vật. Cơ năng dao động của con lắc là bao nhiêu?

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There are different ways to keep fit. One of the most important ways is by exercising. Exercising must be done regularly. The amount of exercise done each time is dependent on the free time that a person has. Exercises can be done from twenty minutes to an hour. Sometimes, daily five-minute exercises are just as effective. Exercising can take place both indoors and outdoors. Those who exercise indoors often do so in the comfort of gymnasiums. They train on equipment that has been specially designed for the different parts of the body. Sometimes, games can also be played indoors. Badminton courts and even some swimming pools are found indoors. There are many different types of outdoor exercises. These include tennis, cycling and even rock climbing. Most people enjoy outdoor activities because they like being in the Sun or are attracted to its sense of peace and quiet. Yet there are others who like the wind blowing against them. Some of these activities are only suitable for people who love adventure. The type of exercise a person takes up often depends on his lifestyle and personality. It is important that a person finds an exercise that is suitable for him. 1. According to the passage, why do some people spend less time exercising? A. Five minutes is effective for them B. They do not have much free time C. Gymnasiums are expensive D. They keep fit not by exercising 2. Which of the following is not a place for indoor exercise as mentioned in the passage? A. Tennis courts B. Badminton courts C. Swimming pools D. Gymnasiums 3. Which statement is TRUE according to the passage? A. People should exercises are more popular then indoor. B. Outdoor exercises are more popular than indoor. C. Rock climbing is suitable for more adventurous people. D. Facilities in gymnasiums are not effective. 4. The highlighted phrase “do so” in the passage refers to…………….. A. take place B. exercise indoors C. exercise outdoors D. train on equipment 5. Which of the following influences the particular type of exercise a person takes up? A. Health B. Income C. Occupation D. Lifestyles