a, \(w=2\pi f=2\pi.5=10\pi\left(\dfrac{rad}{s}\right)\)

\(A=\sqrt{x^2+\left(\dfrac{v}{w}\right)^2}=\sqrt{2^2+\left(\dfrac{20\pi}{10\pi}\right)^2}=2\sqrt{2}\left(cm\right)\)

Lúc t = 0

Trường hợp 1: Vận tốc của vật chuyển động theo chiều âm

 \(\left\{{}\begin{matrix}x=Acos\varphi\\v< 0\end{matrix}\right.\\ \Leftrightarrow\left\{{}\begin{matrix}2=2\sqrt{2}cos\varphi\\v< 0\end{matrix}\right.\\ \Leftrightarrow\varphi=\dfrac{\pi}{4}\)

=> Phương trình dao động: \(x=Acos\left(wt+\varphi\right)=2\sqrt{2}cos\left(10\pi.t+\dfrac{\pi}{4}\right)cm\)

Trường hợp 2: Vận tốc của vật chuyển động theo chiều dương

\(\left\{{}\begin{matrix}x=Acos\varphi\\v>0\end{matrix}\right.\\ \Leftrightarrow\varphi=-\dfrac{\pi}{4}\)

=> Phương trình dao động: \(x=2\sqrt{2}cos\left(10\pi.t-\dfrac{\pi}{4}\right)\)

b, \(v_{max}=wA=10\pi.2\sqrt{2}=20\sqrt{2}\pi\approx88,85\left(\dfrac{cm}{s}\right)\)

\(a_{max}=w^2A=\left(10\pi\right)^2.2\sqrt{2}\approx2791,5\left(\dfrac{cm}{s^2}\right)\)

bạn xem lại đề nha, thiếu vận tốc nè

VII. Complete the following sentences with the correct form of the verbs in the brackets
1. They (watch)..watched.............TV late at night yesterday.
2. Was Your friend (be)..............at your house last weekend?
3. They (not be)....weren't..........excited about the film last night.
4. Yesterday, I (go) ......went..........to the restaurant with a client.
5. Last week, we (drive)......drove........around the parking lot for 20 mins to find a parking space.
6. When we (arrive)......arrived........ at the restaurant, the place (be).....was.... full.
7. My client and I slowly (walk)....walked..........back to the car 3 week ago
8. linh (do)......did........her maths homework yesterday.
9. My mother.....is buying.........(buy) some food at the grocery store at the moment. 
10. Luke....isn't studying..........(not study) Japanese in the library. He's at home with his friends now.
11. ...............Is she running.......................(she, run) down the street at present?
12. My cat........is eating.........(eat) now.
13. Who..are you waiting.(you, wait) for at the moment?
14. Her students......aren't trying........(not/try) hard enough in the competition.
15. All of Andy's friends......are having........ (have) fun at the party right now.
16. My neighbours ..are traveling....(travel) around Europe now.
17. The little girl.......is drinking.......(drink) milk.
18. Listen! Our teacher.......is speaking.......(speak).
19. My friend.......lives.......(live) in London.
20. They (not/study).....don't study......... English at the university.
21. We......play........(play) football every weekend.
22. We......travel........(travel) to different countries every summer.
23. The company......develops........(develop) innovative products to stay ahead in the market.
24. He........works......(work) tirelessly to achieve his goals.
25. I......don't work........(not/work) as a Marketing editor in AHK company.
26. She usually.......goes....... (go) to the gym after work.
27. The cat often (sleep)......sleeps........ on the sofa.
28. He......doesn't like........(not/like) to eat pizza.
29. They........travel......(travel) to different countries every year.
30. We.....have.........(have) lunch at 12 o'clock.
31. Does She never.....read..........(read) a book in the park?
32. He (work).......works....... as a teacher.
33. The train (arrive) ..arrives............at 8 every morning.
34. I think he (not come)........won't come...... back his hometown.
35. I'm afraid I.. ...won't be...........(not/be) able to come tomorrow.
36. Because of the train strike, the meeting (not/ take) .....won't take.........place at 9 o'clock.
37. A: "Go and tidy your room."
B: "Okay. I.....will do.........(do) it now!"
38. We sometimes.(drink)....drink.......... coffee in the morning.
39. They (play) .......play.......the guitar very well.
40. She (not/teach) ..doesn't teach............English at the language center every weekend.
41. She often (study)......studies........ hard so that she can get into a top university.
42. They (do) ....will do.......it for you tomorrow.
43. Sarah(go)....goes.......to the gym every day.
44. My father (call)......will call..... you in 5 minutes.
45. We believe that she (recover)....will recover....... from her illness soon.
46. I promise I (return) ....will return.......school on time.
47. If it rains, he (stay).....will stay......at home.
48. My sister (get)......got.....married last month. 
49. Daisy (come) ......came.............to her grandparents' house 3 days ago
50. My computer (be)..........was.................. . broken yesterday.
51. He (buy)......bought.........me a big teddy bear on my birthday last week.
52. My friend (give)....gave..........me a bar of chocolate when I (be)......was.......at school yesterday.
53. My children (not do) ...didn't do...........their homework last night.
54. Did You (live) .....live............here five years ago?
55. Do You (take) ......take........me to the zoo this weekend?

1. The house need to be sold

2. We suggested that some flowers should be bought for their teacher

8A

10C

5A nha bạn: sau most là danh từ số nhiều, girls vẫn đúng, sửa does => do

1B => biscuits

2A => Did

3A => How much

4C => a bottle

5A => Do

6A => Does

7A => When

8A => fish

9A => what

He bought the shirts immediately instead of asking for a discount

B

Exercise 7

1. She said that she couldn't find her umbrella

2. They said that they were learning English then

3. Tom said that his friend was coming the following week

4. If it didn't rain tomorrow, I wouldn't stay at home to watch TV

5. If I knew English, I could speak to that man

6. If she hadn't stayed at home, I could have met her

7. Her mother hasn't shouted at her for 3 years

8. We didn't have as much stresses as teens nowadays

9. Despite her helpful parents, she tries to do studies herself

10. Because of being tired, he forgot to do his homework