Dùng 1 ròng rọc động và 1 ròng rọc cố định để nâng 1 vật lên cao 15m người ta phải kéo 1 lực ở đầu dây 300N. Tính a)Công phải thực hiện để nâng vật b) Khối lượng của vật. Biết độ lớn của lực cản 20N

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Ex 1. Choose the best word/words in brackets 1. My friend .....................to the museum now. (goes, went, is going) 2. My grandfather ..........................TV at the moment. (watches/ is watching/ was watching) 3. Tom was taking a photograph of me while I .....................(don’t look/ isn’t looking/ wasn’t looking). 4. I .......................... soccer at that time. (am playing/ was playing/play) 5. Look! It’s ......................... (is snowing/ was snowing / snows). Ex 2. Give the correct form of the verbs in the blankets: 6. He ............................... (paint) the ceiling at the moment. 7. Last night I .......................... read in bed when suddenly I heard a scream. ............... ....................... (You/watch) television when I phoned you? 8. Ann ........................ (wait) for me when I arrived. 9. I ..................................... (not/drive) very fast when the accident happened. 10. What ............................. (you/do) at this time yesterday? 11. I saw Carol at the party. She .......................... (wear) a really beautiful dress. 12. When the teacher came in, the pupils ............. ................... (play) games. 13. Excuse me, I ............................ (look) for a phone book. Is there one near here? 14. Listen! Can you hear those people next door? They ........................ (shout) at each other again. Ex 3. Rewrite the sentences: 1. I don’t know anyone in this class.  I wish……….....…………..………….....................….……………………………… 2. The dictionary is very expensive.  I wish……….....…………..………….....................….…………………………….. 3. It’s a pity that my room is too small!  I wish……….....…………..………….....................….…………………………….. 4. She isn’t here.  She wishes ……….....…………..………...........….……………………………….. 5. The students never go abroad.  The students wish ……….....…………..………….................….………………… 6. They cannot eat seafood.  They wish……….....…………..………….....................….……………………….. 7. Their team doesn’t play very well.  They wish……….....…………..………….....................….……………………….. 8. Lien never goes on a camping trip. .  Lien wishes……….....…………..………….....................……………………… 9. I wish I (can) speak English perfectly.  I wish……….....…………..………….....….……………………………………… 10. I wish I (can) do this exercise.  I wish……….....…………..………….....….……………………………………… 11. I wish I (know) how to swim.  I wish……….....………….….....………..………………………………………… 12. I wish the weather (be) better today.  I wish……….....…………..………….....….……………………………………… 13. I wish you (like) my painting.  I wish……….....…………..………….....….……………………………………… 14. I wish I (not have to) work on Saturday.  I wish……….....…………..………….....….……………………………………… 15. I wish you (not come) here late.  I wish……….....…………..………….....….……………………………………… 16. I wish I (will be) there soon.  I wish……….....…………..………….....….………………………………………