15: Pha dao động là pi+pi/2=3/2pi

=>Chọn C

14:

Khi t=1,25 thì \(x=2\cdot cos\left(2.5pi-\dfrac{pi}{6}\right)=1\)

=>Chọn A

15: Pha dao động là pi+pi/2=3/2pi

=>Chọn C

14:

Khi t=1,25 thì \(x=2\cdot cos\left(2.5pi-\dfrac{pi}{6}\right)=1\)

=>Chọn A

16: \(10t-\dfrac{3}{2}pi=\dfrac{2}{3}pi\)

=>10t=2/3pi+3/2pi=13/6pi

=>t=13/60pi

\(x=6\cdot cos\left(10\cdot\dfrac{13}{6}pi-\dfrac{3}{2}pi\right)\)

\(=6\cdot cos\left(\dfrac{2pi}{3}\right)=-3\)

=>Chọn C

10B

x=A*cos(\(\omega t+\varphi\))

x=5*cos(\(\omega t\))

=>A=5

11A:

Biên độ dao động bằng quỹ đạo chia đôi

=>A=MN/2=15cm

12C

\(y=-10\cdot cos\left(4\Pi t-\dfrac{pi}{4}\right)=10\cdot cos\left(4\Pi t+\dfrac{pi}{4}\right)\)

=>Pha dao động ban đầu là pi/4

13C

\(y=-8cos\left(2t+\dfrac{pi}{2}\right)=8\cdot\left[-cos\left(2t+\dfrac{pi}{2}\right)\right]\)

\(=8\cdot cos\left(2t-\dfrac{pi}{2}\right)\)

=>Pha dao động ban đầu là -pi/2

Câu 48: B

Câu 44: D

37 C

38 B

39 D

40 A

37 C

38 C

39 A

40 D

36 C

37 A

38 B

39 D

40 B

36 A

37 A

38 A

39 B

40 D

41. The purpose of this campaign is to ....... money for charity

→ Đáp án:         D. raise 

42. Susan ...... the door, and Peter was waiting for her outside her house

→ Đáp án:         B. answered

43. It's no use fighting those serious infections with ..........

→ Đáp án:         D. pencillin

44. My twin brother is a very ....... person. He plans everything very carefully not only at home but also at work

→ Đáp án:         C. organized

45. It's essential to know to how to ..... campfires before you go camping

→ Đáp án:         D. put out

46. In my family, my mother is the person who ........ breakfast. For lunch and dinner, my sister and I are in charge.

→ Đáp án:         A. makes

47. I don't mind doing the housework, expect .......... the rubbish

→ Đáp án:         C. taking out

48. If you have some water problems, call George. He's an excellent ..............   

→ Đáp án:         A. plumber 

49. Lots of children say that their parents usually .......... them about chores and studying   

→ Đáp án:         B. nag

50. It's very important to show ....... for the elderly

→ Đáp án:         C. respect

51. Located in the Saigon Zoo, .......... has a variety of beautiful tropical kinds of flowers

→ Đáp án:         B. The Botanical Garden

1 C

2 B

3 D

4 B

5 A

6 B

7 B

8 C

9 C

10 A

11 D

12 A

13 C 

14 B

15 C

16 A

17 B

18 D

19 D

20 C

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