21. am doing - think - know

22.  buys

23. rains - is raining 

24. is cooking - cooks

1 am doing - think - know

2 buys

3 rains - is raining

4 is cooking -* cooks

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a: k=3/8

b: y=3/8x

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Bài 1:

b. \(U=IR=I\left(R1+R2\right)=0,4\left(15+2\right)=6,8\left(V\right)\)

c. \(I=I1=I2=\dfrac{U'}{R}=\dfrac{60}{15+2}=\dfrac{60}{17}\simeq3,5\left(A\right)\left(R1ntR2\right)\)

Bài 2:

\(5400kJ=1500\left(Wh\right)\)

a. \(A=Pt\Rightarrow P=\dfrac{A}{t}=\dfrac{1500}{1}=1500\left(W\right)\)

b. \(P=UI\Rightarrow I=\dfrac{P}{U}=\dfrac{1500}{220}=\dfrac{75}{11}\simeq6,82\left(A\right)\)

Bài 3:

a. \(R=p\dfrac{l}{S}=1,1.10^{-6}\dfrac{3}{0,05.10^{-6}}=66\left(\Omega\right)\)

b. \(P=UI=U\left(\dfrac{U}{R}\right)=220.\left(\dfrac{220}{66}\right)=733,33\left(W\right)\)

c. \(A=Pt=733,33.\left(\dfrac{30}{60}\right)=366,665\left(Wh\right)=0,366665\left(kWh\right)=1319994\left(J\right)\)

Bài 4:

a. \(S=\pi\dfrac{d^2}{4}=\pi\dfrac{1^2}{4}=0,785\left(mm^2\right)\)

\(\Rightarrow R=p\dfrac{l}{S}=5,5.10^{-8}\dfrac{10}{0,785.10^{-6}}=\dfrac{110}{157}\simeq0,7\left(\Omega\right)\)

b. \(A=Pt=UIt=U\left(\dfrac{U}{R}\right)t=70\left(\dfrac{70}{0,7}\right).\dfrac{1}{3}=2333,33\left(Wh\right)=2,33333\left(kWh\right)\simeq8400000\left(J\right)\)

4 going to buy a lot of things for the party tomorrow

5 is go out somewhere for a drink

6 Jane going to travel around the world

7 short and fair

8 a good football player

9 a fast runner

10 hard workers

11 swim well

12 worked busily

1 A

2 D

3 C

4 A

5 A

1 C

2 A

3 D

4 A

5 B

6 D

7 C

8 C

II

1 A

2 B

III

1 deaf

2 countless

3 inventor

4 delivery

IV

1 He worked with deaf-mutes at Boston University in America

2 I am going to see the movie Dream city at 6.45 this evening

V

1 going to visit my friends next Sunday

2 go to the movie tonight