问题 多选题

如图所示,一列简谐横波沿x轴正方向传播.t=0时,波传播到x轴上的质点B,在它的左边质点A位于正最大位移处,在t1=0.6s时,质点A第二次出现在负的最大位移处,则(  )

A.该波的速度等于5m/s

B.t1=0.6s时,质点C在平衡位置处且向上运动

C.t1=0.6s时,质点C在平衡位置处且向下运动

D.当E质点第一次出现在最大位移处时,质点A恰好在平衡位置且向上运动

答案

A、由题,t=0.6s时,质点A第二次出现在负向最大位移处,则有1.5T=t,得到周期T=0.4s,由图读出波长为λ=2m,则波速为v=5m/s.故A正确.

B、C,B点与C点间距离等于0.5个波长,则波从B传到C所用时间为0.5T=0.2s,则t1=0.6s时,质点C振动了0.4s=T,而质点C起振方向向上,则t1=0.6s时,质点C在平衡位置处且向下运动.故B错误,C正确.

D、由图看出,A和E的距离等于1

1
4
波长,相当于
1
4
波长,则当质点E第一次出现在正最大位移处时,结合波形可知,质点A恰好在平衡位置且向下运动,故D错误.

故选AC

阅读理解

When my father was getting ready for work, our house was ruled by knocks and words.He used to come downstairs to breakfast.The morning paper lay beside his plate.He always read the “Deaths” first, and then he knocked once on the table.One of my sisters brought his bread, already buttered for him.Usually he said nothing, but once I heard him say, “I love you very much, Edith.I would love more if you buttered my bread on both sides.” He read the paper all through breakfast.Two knocks on the table meant “I am ready for my tea.” If a single knock followed that meant, “More bread, please.”

After breakfast he said, “Boots.” The paper was spread(展开) for him over the back of an arm-chair.Yesterday’s paper was put on the chair for his feet, and his boots were brought to him, freshly cleaned.He read standing at the same time putting on his boots.With one boot finished he said, “Bus.” At that point one of the girls went outside to the garden gate and waited there.Her job was to stop a bus when it came.It came early sometimes and it had to wait for my father.“Overcoat, hat.” One of my sisters had already brushed his overcoat.Now she held it open for him.Another girl came with his hat, nicely brushed.“Handkerchief, pipe(烟斗).” They were brought and put, with his tobacco(烟草), into his pocket.He looked out of the window and said either “Walking stick” or “Umbrella”.It was handed to him.Ready now, he was still reading the paper.He didn’t put it down until he heard the shout “Bus coming!” Then he kissed my mother and went out.The girls breathed freely.

How lucky a man was to have a wife and five daughters at home!

68.When the father made the first knock, he meant _______.

A.he had begun to read the morning newspaper

B.he was made to feel sad by the” Deaths” news

C.he would start to read the other parts of the paper

D.his breakfast should begin

69.What does “Edith” mean?

A.A kind of bread.          B.One of the writer’s sisters.

C.The writer.           D.The writer’s mother.

70.All the daughters were quite busy in the morning because _______.

A.their father never helped them

B.their father always gave different instructions at the same time

C.each of them had to start and finish her job just on time

D.they were not clever or quick enough to do their jobs

71.What was the father’s favorite?

A.Reading newspaper.     B.Having bread buttered on both sides.

C.Giving instructions.      D.Being clean and tidy.

单项选择题