问题 计算题

一艘敌舰正以v1=12 m/s的速度逃跑,执行追击任务的飞机,在距水面高度h=320 m的水平线上以速度v2= 105m/s同向飞行,为击中敌舰,应“提前”投弹。若空气阻力可以不计,重力加速度g取10m/s2,飞机投弹时沿水平方向,它与敌舰之间水平距离应多大?若投弹后飞机仍以原速度飞行,在炸弹击中敌舰时,飞机与敌舰的位置有何关系?

答案

解:投下的炸弹竖直方向上做自由落体运动,水平方向上以飞机的速度v2做匀速直线运动,炸弹在空中飞行的时间为

在8s时间内,炸弹沿水平方向飞行的距离s2=v2t,敌舰在同一方向上运动的距离为s1=v1t,由图可以看出,飞机投弹时水平方向上“提前”距离应为s=v2t-v1t=105×8 m-12×8 m=744 m

在t=8 s时间内,炸弹与飞机沿水平方向的运动情况相同,都以速度v2做匀速直线运动,水平方向上运动的距离都是s2=v2t=840 m。所以炸弹击中敌舰时,飞机恰好从敌舰的正上方飞过

阅读理解

阅读理解。

     Narcissus was a beautiful looking boy. He had long, flowing, blond hair, beautiful, bright, blue eyes and

even, white teeth. Many young ladies fell in love with him including the nymph (女神): Echo.

     Nymphs were lively spirits who lived near streams and lakes and protected trees in the forest. Echo had

upset the Queen of the Gods: Hera. As a punishment Hera made Echo unable to speak except to repeat the

last three words of the person she was talking to.

     Poor Echo fell in love with Narcissus but could never tell him how she felt. Narcissus teased her and she

ran away with tears pouring down her face. Aphrodite, the goddess of love saw what happened and decided

to punish Narcissus. As he came to a pool of water Narcissus saw his reflection (影子) and fell in love with

the vision he saw. It was of course his own reflection.

     Poor Narcissus watched his own reflection, but every time he tried to touch the face of the vision he loved

it broke up on the shimmering surface of the water. Narcissus stopped eating, lost his beautiful looks and

desired to get his love. In the end he anguished gradually and died.

     Aphrodite took pity on him and made a flower grow in his place on the bank of the lake. Narcissus flowers

(水仙花) can be found to this day growing wherever you can find water and trees.

1. Echo fell in love with Narcissus because _____.

A. Narcissus was good-looking

B. Echo was a lively spirit

C. Narcissus loved her, too

D. Echo took pity on Narcissus

2. Why did Aphrodite, the goddess of love, punish Narcissus?

A. Aphrodite envied Echo because she loved Narcissus.

B. She thought Narcissus didn't respect and made Echo sad.

C. Narcissus fell in love with the vision, not Echo.

D. Echo was trapped in love and didn't protect trees in the forest any longer.

3. What does the underlined word "anguished" in the fourth paragraph mean?

A. Become increasingly thin and weak.

B. Become very hungry.

C. Become very fat.

D. Become out of mind. 

4. What is the main purpose of writing the passage?

A. To tell people a sad love story.

B. To tell people how Narcissus flowers came.

C. To tell the true meaning of beauty and ugliness.

D. To tell people not to affect others' love.

单项选择题