`*` Tóm tắt:

\(R=60\Omega\\ I=2A\\ m=2l=2kg\\ t_0=100^oC\\ t_1=25^oC\\ t=15min=900s\\ c=4200J/kg\cdot K\\ ------------\)

`a) mathcalP = ?W`

`b) H=?`

_

`*` Giải:

`a)` Công suất tỏa nhiệt của bếp:

`mathcalP= I^2 * R = 2 * 60=120W`

`b)` Nhiệt lượng thu vào của nước:

\(Q_1=m\cdot c\cdot\left(t_0-t_1\right)=2\cdot4200\cdot\left(100-25\right)=630000J\)

Nhiệt lượng tỏa ra của nước:

\(Q=I^2\cdot R\cdot t=2^2\cdot60\cdot900=216000J\) 

Hiệu suất của bếp:

\(H=\dfrac{Q_1}{Q}\cdot100\%=\dfrac{630000}{216000}\cdot100\%\approx291,67\%.\)

Ta có: \(L=\dfrac{N}{2}\cdot3,4\Rightarrow N=\dfrac{L\cdot2}{3,4}=\dfrac{5100\cdot2}{3,4}=3000\left(nu\right)\)

Ta có: \(T=20\%\cdot3000=600\left(nu\right)\)

Mà: \(A=T=600;G=X\)

Ta có: \(N=A+T+G+X\)

\(\Rightarrow N=2A+2G\\ \Rightarrow3000=\left(2\cdot600\right)+2G\\ \Rightarrow2G=3000-1200\\ \Rightarrow2G=1800\\ \Rightarrow G=\dfrac{1800}{2}=900\left(nu\right)\)

Vậy: \(T=A=600nu;G=X=900nu.\)

`21.=>` Mr. David said to Mrs. Laura that his son would be there soon.

`22.=>` Mai said to Jack that she was going to visit Jack's grandmother with her mother.

`23.=>` Aunt Hoa said to Tuan that she was happy to see he there.

`24.=>` My friend said that my friend was having a wonderful time with my friend's husband in Nha Trang then.

`25.=>` They said that they have plenty of time to do their work.

`26.=>` The teacher said to us that they might choose any subject that they like best.

`23. =>` His friend asked Mr. Parker how he had got to the bus stop the previous day. 

`24.=>` Tu asked me if I had visited Mui Ne, Ca Mau Province.

`25.=>` Long asked me if I was keen on reading that novel.

III.

`1.=>` Tom asked me if I was going to visit my aunt the next day.

`2.=>` Johnny asked his grandmother they would read those fairy tales before bedtime.

`3.=>` The woman asked John if she might ask he a few questions.

`4.=>` Martha asked her brother where he was going on his birthday.

`5.=>` Nicky said that he didn't know where Bill was living then.

`6.=>` Miss Baker said to us that they had to do their homework every day. 

`7.=>` Susan said that her parents left for London at 5p.m the previous day.

`8.=>` The teacher asked me if I had to done my project about space exploration.

`9.=>` Mr. Bao asked Lan if often she wrote letters to her pen pal.

`10.=>` Lien asked me what I was going to buy then.

`11.=>` I asked the Browns if the Browns were having a barbecue that night.

`18.=>` Mary said that she couldn't go to the theater with Jonh that night.

`19.=>` My father said that he might visit his friends that summer holiday.

`20.=>` The teacher said to his students that they could donate their old books to street children there.

`21.=>` Mr. Hai told Mai that he would tell she about Hoa's secret the next day. 

`22.=>` Nick said to Sarah that he might see she the following week before he leave. 

`23.=>` Matt said that he had not attended the meeting two days before.

`24.=>` Duc asked Trang if she knew NASA has found two new plantets.

`12.=>` A tourist asked Mali if Mali knew where was the nearest post office. 

`13.=>` My friend told me if I was going to visit my aunt in Da Nang the next day.

`14.=>` Tam's friends asked her if she wanted to stay at a hotel or in her friend's home in Paris.

`15.=>` Mrs. Brown asked Thu what language she spoke. 

`16.=>` She asked me if I was meeting Judy at four o'clock that day.

`17.=>` Mrs. Le asked Mr. Dung how often he visited his parents.

Thì ý kiến đó, biết anh ấy ra sao rồi vẫn tiếp tục thích thì là cố chấp không muốn tin, biết bản thân phải như nào sẽ hết buồn mà không muốn làm. 

Trả lời từ đời nào rồi vẫn đào lên lại.

Số công nhân đắp đoạn đường đó trong 1 ngày là:

`12 xx 7 = 84` (công nhân)

Số công nhân đắp đoạn đường đó trong 4 ngày là:

`84 : 4 = 21` (công nhân) 

Số công nhân đến thêm là:

`21 - 12 = 9` (công nhân)

Đáp số: `9` công nhân.

`-` TN: Ngoài khơi xa `->` Chỉ nơi chốn.

`-` CN: tiếng sóng.

`-` VN: vỗ ầm ầm.