问题 计算题

(9分) 如图所示, 在距地面80 m高的水平面上做匀加速直线运动的飞机上每隔1 s依次放下M、N、P三物体, 抛出点a、b与b、c间距分别为45 m和55 m, 分别落在水平地面上的A、B、C处, g取10 m/s2。 求:

(1)飞机飞行的加速度;

(2)刚放下N物体时飞机的速度大小;

(3)N、P两物体落地点B、C间的距离。

答案

(1)10 m/s2 (2)50 m/s (3)95 m

(1)飞机在水平方向上, 由a经b到c做匀加速直线运动, 由Δs=a0T2得,

a0=10 m/s2.

(2)因位置b对应a到c过程的中间时刻, 故有

vb=50 m/s.

(3)设物体落地时间为t,

由h=gt2

得: t= =4 s

BC间的距离为: BC=bc+vct-vbt

又vc-vb=a0T

得: BC=bc+a0Tt=95 m.本题考查匀变速直线运动推论的应用,在匀变速直线运动过程中经过相邻的相等的时间内通过的位移差值恒定不变,由Δs=a0T2可求得加速度大小,b点为a、c间的中间时刻,由中间时刻的瞬时速度等于平均速度可求得b点速度大小,自由落体运动中由公式Δs=a0T2可求得BC段距离

阅读理解

阅读理解。

     How can you buy a meal for lunch without any money in your pocket? Students in Class 9, Grade 8 at

Mountain and Lake Middle School in Chengdu,Sichuan,have their ways. They give out flyers (传单), draw

portraits (人物素描) and work as waiters.

     The class, working in eight groups, finished the activity. Experiencing Life for Seven Hours,on March 18,

"I found students waste their food in the dining-hall," the class teacher, Deng Guiyong said, "So I held this

activity to help them understand how hard it is to make money."

     Jiang Yao, 15, and his group members stood in the streets giving out flyers for about two hours and got

the money for their lunch. Then they worked as waiters in a pizza restaurant-cleaning the floor;and toilets

and getting food for guests,"We were busy all along, so we were terribly exhausted after the day's hard work.

"said Jiang."We each got a pizza as a prize, which tasted much better than one I ate with my parents before."

     When Xie Ni's group didn't make any money in three hours, the members became nervous about their

lunch. The 14-year-old girl came up with the idea of drawing portraits to sell, "I sold four portraits and one

tourist even paid us 100 yuan for his portrait," said Xie.

     Xie realized that life is really hard. "We have to work hard to get the money to pay for even a simple meal."

Xie said, "We must value the happy life today."

     On top of making money, each group was asked to do at least five good deeds during the seven hours.

Students helped the old cross the road, gave directions to tourists and turned in a lost bus card.

1. From the teacher's words, we can see that the students ________.

A. usually waste food in their daily life

B. realize life is really not easy

C. know it's hard to make money

D. have their own ways to get food without money

2. The underlined word "exhausted" in Paragraph 3 means ________.

A. happy

B. crazy

C. tired

D. boring

3. In order to make money, the students have done all except ________.

A. help the old cross the road

B. give out flyers

C. draw portraits

D. work as waiters

4. The purpose of this activity is to ________.

A. let the students get food

B. help the students learn to value their today's life

C. help people in need

D. give the students a chance to learn to work

5. What's the best title for the passage?

A. Life Is Really Hard

B. It's Good To Be A Volunteer

C. How To work For People

D. Experiencing Life For Seven Hours

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