问题 选择题

一小船在静水的速度为3m/s,它在一条河宽150m,水流速度为4m/s的河流中渡河,则该小船(  )

A.能到达正对岸

B.渡河的时间可能少于50s

C.以最短时间渡河时,它沿水流方向的位移大小为200m

D.以最短位移渡河时,位移大小为150m

答案

A、因为船在静水中的速度小于河水的流速,由平行四边形法则求合速度不可能垂直河岸,小船不可能垂直河岸正达对岸.故A错误.

B、当船的静水中的速度垂直河岸时渡河时间最短:tmin=

d
v
=50s,故B错误.

C、船以最短时间50s渡河时沿河岸的位移:x=vtmin=4×50m=200m,即到对岸时被冲下200m,故C正确.

D、因为船在静水中的速度小于河水的流速,由平行四边形法则求合速度不可能垂直河岸,小船不可能垂直河岸正达对岸.

所以最短位移大于河的宽度即大于150m.故D错误.

故选C.

阅读理解

This was the first real task I received in my new school. It seemed simple: go on the Internet and find information about a man named George Washington. As I searched the name, I found that there were two famous people having the same name who looked completely different! One invented hundreds of uses for peanuts(花生), while the other led some sort of army across America. I stared at the screen, wondering which one my teacher meant. I called my grandfather for a golden piece of advice; let the coin decide. I flipped(掷) a coin and Ah! Tails (背面)! My report would be about the great man who invented peanut butter, George Washington Carver.

Weeks later, I stood in front of the classroom and proudly read my homework. But things started to get strange. I looked around the room, only to find my classmates with big smiles on their faces and tears in their eyes and my stone-faced teacher. I was completely lost. “What could be causing everyone to act this way?”

Oh well, I dropped the paper and sat down at my desk, burning to find out what I had done wrong. As a classmate began his report, it all became clear, “My report is on George Washington, the man who started the American War of Independence.” The whole world became quiet! How could I know that my teacher meant that George Washington?

Of course, my subject result was awful. Sad but fearless, I decided to turn this around. I talked to the headmaster Miss Lancelot, but she said firmly: No re-dos; no new score. I felt that it was not fair, and I believed I deserved a second chance. So I threw myself heartily into my work for the rest of the school year. Ten months later, I sat in the headmaster’s office again, but this time a completely different conversation. I smiled and flashed back to the terrible moment at the beginning of the year as the headmaster told me I was good enough to skip(跳过) the 6th grade and started the 7th grade next term.  

小题1:The task I received was to find information about ________.

A.uses for peanuts

B.American War of Independence

C.George Washington

D.my headmaster Miss Lancelot小题2:________ helped me decide what my report would be about.

A.The Internet

B.My classmates

C.My grandpa

D.A coin小题3:People in the class acted strangely because ________.

A.I was too proud of my homework

B.I mistook what the homework was about

C.the whole world suddenly became quiet

D.the teacher’s face turned to a stone小题4:I ________ after I failed the subject.

A.worked harder to prove my ability

B.started to study from the 7th grade

C.was so frightened at the awful result

D.was given a second chance to redo the work小题5:We can infer(推断) from the passage that ________.

A.the headmaster didn’t like the writer at all

B.the writer’s classmates felt sad at his mistake

C.the writer knew little about American history

D.the writer’s grandpa was a very wise man小题6:Which of the following proverbs can best describe the main idea of this story?

A.Seeing is believing.

B.Where there is a will, there is a way.

C.One is never too old to learn.

D.A friend in need is a friend indeed.

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