如图所示装置的机械效率为80%,物体A在拉力F作用下以60cm/s的速度在水平面

题型:问答题

问题:

如图所示装置的机械效率为80%,物体A在拉力F作用下以60cm/s的速度在水平面上移动,已知物体A重200N,运动时所受到的阻力是80N,求拉力F的功率.

考点:功率的计算滑轮(组)的机械效率
题型:问答题

已知等腰三角形的一内角度数为100,则这个等腰三角形的顶角度数为[ ]

A.40

B.80

C.100

D.40或100

题型:问答题

下列离子方程式中,正确的是(    )  

A.NH4HSO3溶于少量NaOH溶液中: HSO3-+OH= SO32-+H2O

B.酸性KMnO4溶液与双氧水反应: 2MnO4-+ 7H2O2 + 6H+= 2Mn2+ + 6O2↑+ 10H2O

C.向氯化银悬浊液中滴入饱和碘化钾溶液:Ag++ I= AgI ↓

D.标准状况下672mL Cl2通入100mL0.1 mol·L-1FeBr2溶液中:2Fe2+2Br+2Cl2=2Fe3+Br2+4Cl

题型:问答题

恼怒常引起何证 ()

A.癫病

B.狂病

C.郁病

D.气厥实证

E.血厥实证

题型:问答题

乙醇是一种重要的有机化工原料,它可以用玉米、薯类等为原料经发酵、蒸馏制成。乙醇和汽油经加工处理形成的车用燃料即乙醇汽油。

结合有关知识,回答下列问题:

(1)乙醇分子中的官能团是     (填写名称)。

(2)试写出实验室用乙酸和乙醇在浓硫酸催化作用下共热反应生成乙酸乙酯的化学方程式                        

题型:问答题

阅读理解。

     Robert Spring, a 19th century forger (伪造者), was so good at his profession that he was able to

make his living for 15 years by selling false signatures of Americans. Spring was born in England in 1813

and arrived in Philadelphia in 1858 to open a bookstore. At first he became rich by selling his small but

real collection of early U.S. autographs (手稿). Discovering his ability at copying handwriting, he began

imitating signatures of George Washington and Ben Franklin and writing them on the title pages of old

books. To lessen the chance of detection (察觉), he sent his forgeries to England and Canada for sale.

     Forgers have a hard time selling their products. A forger can't deal with a respectable buyer but

people who don't have much knowledge in the field. Forgers have many ways to make their work look

real. For example, they buy old books to use the aged paper of the title page, and they can treat paper

and ink with chemicals.

     In Spring's time, right after the Civil War, Britain was still fond of the Southern states, so Spring

invented a respectable maiden lady known as Miss Fanny Jackson, the only daughter of General

"Stonewall" Jackson. For several years Miss Fanny's financial problems forced her to sell a great number

of letters and manuscripts. Spring had to work very hard to satisfy the demand. All this activity did not

prevent Spring from dying in poverty, leaving sharp-eyed experts the difficult task of separating his

forgeries from the originals.

1. Why did Spring sell his false autographs in England and Canada?

A. There was a greater demand there than in America.

B. There was less chance of being detected there.

C. Britain was Spring's birthplace

D. The prices were higher in England and Canada.

2. After the Civil War, there was a great demand in Britain for            

A. Southern money          

B. signatures of George Washington and Ben Franklin

C. Southern manuscripts and letters      

D. Civil War battle plans

3. Robert Spring spent 15 years          .

A. running a bookstore in Philadelphia      

B. keeping in touch with Miss Fanny Jackson

C. as a forger                          

D. as a respectable dealer

4. According to the passage, forgeries are usually sold to        .

A. sharp-eyed experts  

B. persons who aren't experts

C. book dealers        

D. owners of old books

更多题库