问题 填空题

2007年我国在实施探月工程中,若探月飞船在飞向月球的过程中,经过月、地间的引力平衡点P(飞船在P点所受的地球引力与月球引力的合力为零).已知月球与地球质量之比为m:m=1:81,月地距离为3.8×105km,则P点与月球的距离为______km.若人类不断地对月球进行各种探测,计划将来把月球上的矿产搬到地球上.设想经过一段时间的开采后月球的质量减少,这将造成地球对月球的引力将______.(填“变大”、“变小”或“不变”)

答案

设月球质量为M,地球质量就为81M.

飞行器距地心距离为r1,飞行器距月心距离为r2

由于地球对它的引力和月球对它的引力相等,根据万有引力定律得:

G

81Mm
r21
=G
Mm
r22

解得:

r1
r2
=
9
1

而r1+r2=3.8×105km

故r2=3.8×104km;

把月球上的矿产搬到地球上,会是地球与月球质量的乘积变小,故万有引力减小;

故答案为:3.8×104,变小.

单项选择题
阅读理解

阅读理解。

     In a six-week study, experts found people who played online games designed to improve their cognitive

(认知的) skills didn't get any smarter.

     More than 8,600 people aged 18 to 60 were asked to play online brain games designed by the researchers

to improve their memory, reasoning and other skills for at least 10 minutes a day, three times a week. They

were compared to more than 2,700 people who didn't play any brain games, but spent a similar amount of

time surfing the Internet and answering general knowledge questions. All participants were given a sort of

I.Q test before and after the experiment.

     Researchers said the people who did the brain training didn't do any better on the test after six weeks than

people who had simply been on the Internet. On some sections of the test, the people who surfed the Net

scored higher than those playing the games.

     "If you're (playing these games) because they're fun, that's absolutely fine," said Adrian Owen, the study's

lead author. "But if you're expecting (these games) to improve your I.Q., our data suggests this isn't the case,"

he said during a press briefing on Tuesday.

     One maker of brain games said the company's games have been proven to boost brain power. "Their

conclusion would be like saying, 'I cannot run a mile in under 4 minutes and therefore it is impossible to do

so," Aldrich said in a statement.

     "There is precious little evidence to suggest the skills used in these games transfer to the real world," said

Art Kramer, who was not linked to the study and has no ties to any companies that make brain training games.

     Instead of playing brain games, Kramer said people would be better off getting some exercise. He said

physical activity can spark (激发) new connections between nerves and produce new brain cells."Fitness

changes the building blocks of the brain's structure," he said.

1. It can be inferred that the online brain games mentioned in the text are _______.

A. costly

B. unreliable

C. illegal

D. effective

2. Which of the following statements is true about the experiment in the second paragraph?

A. The experiment lasted for a week.

B. Age didn't affect the result of the research.

C. Every person played online brain games three times a day.

D. People who didn't play online brain games did better in I.Q test

3. What can we learn from the text?

A. Playing games which are fun can improve your I.Q.

B. There is a lot of evidence to suggest skills can transfer to the real world.

C. Do physical activity can boost your brain power.

D. Playing online games can spark new brain cells

4. The underlined sentence suggests that ______.

A. The research was not linked to the study

B. Those playing the games can score higher in the test

C. playing the games can spark new connections between nerves

D. This isn't the case that these games can improve your I.Q.