Exercise 1: Write at, in or on to complete these sentences.
1.  I'll see you _____on______ Monday.
2. I met him ____in_______the holidays.
3. I'll pick you up _____at______eight o'clock.
4. I'm going home ______at_____ four.
5. They came to visit us______on_____ my birthday.
6. I can work ______in_____ the morning but I don't like working
night.
7. Did you have a good time ______at_____ Christmas?
8. School finishes ______at_____ three o'clock _____on______ Thursdays.
9. We arranged to meet _______at____ seven ___in________ the morning.
10. We had a party _____on______ the last day of the course.
11. I often go skiing _____in______ winter.
12. What time do you get back ___on________ Tuesday?
13. She's going to visit her parents ____at_______ Easter.
14. He was born ____in_______ 8th June 1968.
15. Stuart can come and see you ____at_______ lunchtime.
16. I always send my wife flowers _______in____ our wedding anniversary.
17. The conference is ____in_______ July.

Bài 39:

a. Ý nghĩa:

Con số này cho biết cứ 1 đoạn dây đồng dài \(1m\) và tiết diện là \(1m^2\) thì sẽ có điện trở là \(1,7\cdot10^{-8}\Omega\)

b. Ta có: \(m=DV=DSl\)

\(\Rightarrow l=\dfrac{m}{DS}=\dfrac{0,5}{8900\cdot1\cdot10^{-6}}\approx56,17m\)

c. Điện trở cuộn dây:

\(R=p\dfrac{l}{S}=1,7\cdot10^{-8}\dfrac{56,17}{1\cdot10^{-6}}\approx0,95\Omega\)

Quãng đường bay từ A:

\(v_2=\sqrt{v^2-v_1^2}=\sqrt{54^2-27^2}=27\sqrt{3}\left(\dfrac{km}{h}\right)\)

Thời gian bay từ A:

\(t_1=\dfrac{s_1}{v_2}=\dfrac{6}{27\sqrt{3}}=\dfrac{2\sqrt{3}}{27}\left(h\right)\)

Quãng đường bay về A:

\(v_2'=\sqrt{v'^2-v_1^2}=\sqrt{45^2-27^2}=36\left(\dfrac{km}{h}\right)\)

Thời gian bay về A:

\(t_2=\dfrac{s_2}{v_2'}=\dfrac{6}{36}=\dfrac{1}{6}\left(h\right)\)

\(\Rightarrow v_{tb}=\dfrac{s_1+s_2}{t_1+t_2}=\dfrac{6+6}{\dfrac{2\sqrt{3}}{27}+\dfrac{1}{6}}\approx40,68\left(km.h\right)\)

Có bạn nào ủng hộ mình hong ta :3

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