问题 问答题

一只船在海上行驶,船上发出一鸣笛声,旅客在4s后听到前方悬崖反射回来的声音,问:

(1)如果船鸣笛后马上停止行驶,求悬崖与船的距离.

(2)若鸣笛的同时,船以20m/s的速度继续向前行驶,求悬崖与旅客听到回声处的距离?(气温为15℃)

答案

(1)t=

1
2
×4s=2s,

∵v=

s
t

∴悬崖与船的距离s=vt=340m/s×2s=680m.

(2)在t=4s的时间内,车行驶的距离:

s1=v1t=20m/s×4s=80m,

声音传播的距离:

s2=v2t=340m/s×4s=1360m,

设司机鸣笛时车到山崖的距离为s,

则:2s=s1+s2,所以s=

s1+s2
2
=
80m+1360m
2
=720m,

(2)司机听到回声车距山崖的距离:

s′=s-s1=720m-80m=640m.

答:(1)如果船鸣笛后马上停止行驶,悬崖与船的距离为680m.

(2)悬崖与旅客听到回声处的距离为640m.

选择题
阅读理解

     A new study of 8,000 young people in the Journal of Health and Social Behavior shows that

although love can make adults live healthily and happily, it is a bad thing for young people. Puppy

love(早恋) may bring stress for young people and can lead to depression(忧郁症). The study shows

that girls become more depressed than boys, and younger girls are the worst of all.

     The possible reason for the connection between love and higher risk of depression for girls is "loss

of self". According to the study, even though boys would say "lose themselves in a romantic

relationship", this "loss of self" is much more likely to lead to depression when it happens to girls. Young

girls who have romantic relationships usually like hiding their feelings and opinions. They won't tell that to

their parents. 

      Dr. Marianm Kaufman, an expert on young people problems, says 15% to 20% young people will

have depression during their growing. Trying romance often causes the depression.

     She advises kids not to jump into romance too early. During growing up, it is important for young

people to build strong friendships and a strong sense of self. She also suggests the parents should

encourage their kids to keep close to their friends, attend more interesting school activities and spend

enough time with family.

     Parents should watch for signs of depression—eating or mood changes—and if they see signs from

their daughter or son, they need to give help. The good news is that the connection between romance

and depression seems to become weak with age. Love will always make us feel young, but only maturity(成熟) gives us a chance to avoid its bad side effects.

1. What's the main idea of the passage?

A. Romance is a two-edged sword for adults  

B. Parents should forbid their children's love lives.  

C. Puppy love may bring young people depression.  

D. Romance is good for young people.

2. Which of the following is more likely to have depression?  

A. Young girls who always hide their feelings and opinions.  

B. Young boys whose parents watch for their behavior.  

C. Young people who have a strong sense of self.  

D. Careless parents whose children are deep in love.

3. What can be inferred from the passage?  

A .Lacking love can lead young people to grow up more quickly.  

B. The older a woman is, the less likely she seems to lose herself in romance.  

C .Parents should help their children to be aware of the signs of depression.  

D. Early love makes young people keep close to their friends and parents.

4. What's the author's attitude towards puppy love?

A. Confused.

B. Scared.

C. Disinterested.

D. Disapproving.