Một động cơ có công suất tiêu thụ bằng 5kW kéo một vật có trọng lượng 12kNlên cao 30 m theo phương thẳng đứng trong thời gian 90 giây với vận tốc không đổi khi hiệu suất của động cơ này ?

Một ô tô có khối lượng 20 tấn chuyển động chậm dần đều trên đường nằm ngang dưới tác dụng của lực ma sát với hệ số ma sát = 0,3 vận tốc đầu của ô tô là 54 km/h sau một khoảng ô tô dừng . A. Tính công và công suất trung bình của lực ma sát trong thời gian đó B. Tính quãng đường ô tô đi được trong khoảng thời gian đó

Một ô tô có khối lượng 2 tấn đang chuyển động thẳng đều với vận tốc 36 km/h trên một đường thẳng nằm ngang hệ số ma sát giữa bánh xe và mặt đường là 0,02 tìm A. Độ lớn của lực phát động B. Công của lực phát động thực hiện trong khoảng thời gian 30 phút C. Công suất của động cơ

Một xe tải có khối lượng 2,5 tấn bắt đầu chuyển động thẳng nhanh dần đều . Sau khi đi được quãng đường 144 m thì xe đạp vận tốc 12 m/s . Biết hệ số ma sát giữa xe và mặt đường là 0,04 4 lấy g=10m/s² A. Tính công của các lực tác dụng lên xe trên quãng đường 144 m đầu tiên B. Tính công suất của lực dao động cơ xe hoạt động ở quãng đường nói trên C. Hiệu suất hoạt động của động cơ xe tải

II. Choose the best answer. 26. James……..the news as soon as possible. ​A. should tell B. should be told ​C. should told D. should be telled 27. My wedding ring ______ yellow and white gold. ​A. is made B. is making C. made D. make 28. Mr. Wilson is _______ as Willie to his friend. A. known B. knew C. is known D. know 29. References _____ in the examination room. ​A. not are used ​B. is not used ​C. didn’t used D. are not used 30. Laura ______ in Boston. A. are born B. were born ​C. was born D. born 31. His car needs ________. A. be fixed ​B. fixing C. to be fixing ​D. fixed 32. Her watch needs _______.A. repairing B. to be repaired C. repaired D. A and B 33. My mother is going _____ this house. A. sold ​B. sell C. to be sold​D. to sell 34. There’s somebody behind us. I think we are _______. ​A. being followed ​B. are followed ​C. follow D. following 35. Have you _____ by a dog? A. bite B. bit C. ever been bitten D. ever been bit 36. The room is being _____ at the moment. A. was cleaned B. cleaned C. cleaning​D. clean 37. It _____ that the strike will end soon. ​A. is expected ​B. expected ​C. are expected D. was expected 38. It is _____ that many people are homeless after the floods. ​A. was reported ​B. reports ​C. reported​D. reporting 39. He was said _____ this building. ​A. designing ​B. to have designed ​C. to design​D. designed 40. Ted ______ by a bee while he was sitting in the garden. ​A. got sting ​B. got stung ​C. get stung​D. gets stung 41. These tennis courts don’t _____ very often. Not many people want to play. ​A. got used ​B. used ​C. get used​D. get use 42. I’ll get Minh _____ do this for you. A. do ​B. done ​C. did​D. to do 43. Those letters ________ now. You can do the typing later. A. need typing ​B. needn't be typed ​C. need to type D. needn't typing 44. “What a beautiful dress you are wearing”- “thanks, it_____ especially for me by a French tailor.” A. is made ​B. has made ​C. made D. was made 45. Somebody cleans the room every day. ​A. The room everyday is cleaned. ​B. The room is every day cleaned. ​C. The room is cleaned every day. D. The room is cleaned by somebody every day. 46. People don’t use this road very often. ​A. This road is not used very often. ​B. Not very often this road is not used. ​C. This road very often is not used. ​D. This road not very often is used. 47. How do people learn languages? ​A. How are languages learned? ​B. How are languages learned by people? ​C. How languages are learned? ​D. Languages are learned how? 48. Over 1500 new houses _______ each year. Last year, 1720 new houses _______. ​A. were built/ were built ​B. are built/ were built​ ​C. are building / were built​D. were built/ were being built 49. Tom bought that book yesterday. ​A. That book was bought by Tom yesterday. B. That book was bought yesterday by Tom. ​C. That book yesterday was bought by Tom ​D. That book was bought yesterday. 50. The new computer system _____ next month. ​ ​A. is be install​B. is being installed C. is been installed D. is being installed by people Giúp mik nha

Cho biểu thức P= cănx-1/x+8. Tính GTLN của biểu thứcP

Hoà tan m gam Cu vào 80ml dd hno3 loãng 1M thoát ra V lít khí và dung dịch B tính m và v và m gam muối sau khi cô cạn dd B . Nhiệt phân muối lên thì thu được m gam

II. Choose the best answer. 1. We can’t go along here because the road........................ ​A. is repairing​B. is repaired​C. is being repaired​D. repairs 2. The story I’ve just read...................Agatha Christie ​A. was written​B. was written by​C. was written from​D. wrote by 3. I’m going to go out and................................................. ​A. have cut my hair​B. have my hair cut​C. cut my hair D. my hair be cut 4. Something funny ...........................in class yesterday ​A. happened​B. was happened​C. happens​D. is happened 5. Many US automobiles........................in Detroit, Michigan ​A. manufacture​B. have manufactured​C. are manufactured D. are manufacturing 6. A lot of pesticide residue can.........................................unwashed produce ​A. find​B. found​C. be finding​D. be found 7. We..................by a loud noise during the night ​A. woke up​B. are woken up​C. were woken up D. were waking up 8. Some film stars...................difficult to work with A. are said be​B. are said to be​C. say to be​D. said to be 9. Why did Tom keep making jokes about me? – I don’t enjoy........................at ​A. be laughed​B. to be laughed​C. laughing D. being laughed 10. Today, many serious childhood diseases...........................by early immunization ​A. are preventing​B. can prevent​C. prevent D. can be prevented 11. Do you get your heating..........................every year? ​A. checking​B. check​C. be checked​D. checked 12. Bicycles.......................in the driveway ​A. must not leave​B. must not be leaving​C. must not be left D. must not have left 13. Beethoven’s Fifth Symphony.......................next weekend ​A. is going to be performed B. has been performed C. will be performing D. will have perform 14. All bottles......................................before transportation ​A. frozen​B. were froze​C. were frozen​D. are froze 15. ...............................................yet? A. Have the letters been typed​B. Have been the letters typed ​C. Have the letters typed​D. Had the letters typed 16. English has become a second language in countries like India, Nigeria or Singapore where.................for administration, broadcasting and education ​A. is used​B. it is used​C. used​D. being used 17. The telephones..............by Alexander Graham Bell ​A. is invented​B. is inventing​C. invented​D. was invented 18. Lots of houses...................by the earthquake ​A. are destroying​B. destroyed​C. were destroyed​D. is destroyed 19. Gold.........................in California in the 19th century ​A. was discovered​B. has been discovered​C. was discover D. they discover 20. The preparation.......................by the time the guest............................ ​A. had been finished- arrived​B. have finished- arrived ​C. had finished-were arriving​D. have been finished- were arrived 21 The boy_____ by the teacher yesterday. A. punish B. punished C. punishing D. was punished 22. “Ms Jones, please type those letters before noon”_ “They’ve already ______, sir. They’re on your desk.” A. typed​B. been being typed ​C. being typed ​D. been typed 23. Sarah is wearing a blouse. It___________ of cotton. ​A. be made B. are made ​C. is made D. made 24. They had a boy _______ that yesterday. A. done ​B. to do C. did D. do 25. We got our mail ______ yesterday. A. been delivered B. delivered C. delivering D. to deliver ——————————————— Giúp e với ah. Cảm ơn mn nhìu

Cho mình hỏi. Câu tạo của phép so sánh là sao ạ.

nếu không lao động và sáng tạo thì sao ??