Bài 2 : Để kéo một vật nặng 50 kg lên cao 8m bằng hệ thồng gồm 1 ròng rọc động và một ròng rọc cố định. a , Vẽ sơ đồ của hệ thống ròng rọc. b , Tính công của trọng lực và công lực kéo. c , Thực tế người đó phải kéo dây với một lực 320N . Tính hiệu suất ròng rọc?

Các câu hỏi liên quan

3. My father was in Ha Noi three weeks ago. . .......................................................................................................................................... 4. Nam played badminton with Minh. . .......................................................................................................................................... 5. She went to the doctor because she had a backache. . .......................................................................................................................................... 6. The students are practicing their English at the moment. . .......................................................................................................................................... 7. He had an appointment at 10.30. . .......................................................................................................................................... 8. They travelled to the USA by plane last month. . .......................................................................................................................................... 9. No. I don’t really like cartoons. I prefer movies. . .......................................................................................................................................... 10. I’d love to. I really like pop music. . .......................................................................................................................................... III. Change into negative and interrogative form: 1. Her mother wrote a sick note for her. . .......................................................................................................................................... . .......................................................................................................................................... 2. Nam was absent from school yesterday. . .......................................................................................................................................... . .......................................................................................................................................... 3. I had a bad cold two days ago. . .......................................................................................................................................... . .......................................................................................................................................... 4. Many students caught flu last month. . .......................................................................................................................................... . .......................................................................................................................................... 5. They were happy with their life. . .......................................................................................................................................... . .......................................................................................................................................... 6. He suggested going out for dinner. . .......................................................................................................................................... . .......................................................................................................................................... 7. I was busy last Sunday. . .......................................................................................................................................... . .......................................................................................................................................... 8. We enjoyed our summer vacation. . .......................................................................................................................................... . .......................................................................................................................................... 9. Children should spend little time playing video games. . .......................................................................................................................................... . .......................................................................................................................................... 10. We often play table tennis together. . .......................................................................................................................................... . ........................................................................................