“勇气”号探测器离火星地面12m时与降落伞自动脱离，被众气囊包_爱下问搜题

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问题问答题

“勇气”号探测器离火星地面12m时与降落伞自动脱离，被众气囊包裹的探测器竖直下落到地面后又弹跳到5层楼的（以15m进行计算）高度，这样上下碰撞了20多分后，才静止在火星表面上．已知火星半径为地球半径的二分之一，质量为地球的

1

9

（取地球表面的重力加速度为10m/s²，计算结果均取两位有效数字）．

（1）若探测器第一次碰到火星地面时其机械能损失为探测器12m高处机械能的10%，不计空气的阻力，求探测器在12m高处的速度．

（2）已知探测器和气囊的总质量为200kg，设与地面第一次碰撞时气囊和地面接触时间为0.4s，求探测器与火星碰撞时所受到的平均冲力？

答案

（1）设探测器在12m高处向下的速度为v_火，则有

1

2

mv火2+mg火h1-mg火h2=0.1×(

1

2

mv火2+mg火h1)

在星球表面处有

GMm

R2

=mg，

可得

g火

g地

=

M火R地2

M地R火2

=

4

9

联立解得v_火=6.4m/s

（2）设探测器与火星碰前瞬间的速度为v₁，反弹的速度为v₂，则有

v12=v火2+2g火h1

v22=2g火h2

规定向上为正方向，对探测器由动量定理可得

（F-mg_火）t=mv₂-mv₁

解以上各式得F=1.3×10⁴N

答：（1）若探测器第一次碰到火星地面时其机械能损失为探测器12m高处机械能的10%，不计空气的阻力，则探测器在12m高处的速度为6.4m/s．

（2）已知探测器和气囊的总质量为200kg，设与地面第一次碰撞时气囊和地面接触时间为0.4s，则探测器与火星碰撞时所受到的平均冲力为1.3×10⁴N．

完形填空

阅读下面短文,掌握其大意,然后从 21～40 各题所给的四个选项(A、B、C和D)中,选出最佳选项,并在答题纸上将该选项标号涂黑。
School was over and I felt quite tired. I sat at the very 21 of the crowded bus because of my anxiety to get home. Sitting there makes me 22 out like a shiny coin in a pile of dull pennies.
Janie, the 23_ , tries to break the uncomfortable atmosphere by striking the match of _ 24 .
I tried to mind my manners and 25 listen, but usually I am too busy thinking about my day. On this day, 26 , her conversation was worth listening to.
“My father’s sick,” she said to no one in 27 , I could see the anxiety and fear in her eyes. “What’s wrong with him?” I asked. With her eyes wet and her voice tight from 28 the tears, she answered, “Heart trouble.” Her eyes 29 as she continued. “I have already lost my mum, so I don’t think I can stand l

osing him.”
I was 30 . My heart ached for her. And this reminded me of the great 31 that my own mother was thrown into when her father died. I saw how hard it was, and 32 is, for her. I wouldn’t like anyone to 33 that.
Suddenly I realized Janie wasn’t only a bus driver. That was 34 her job. She had a whole world of 35 and concerns, too. I suddenly felt very __36____. I realized I had only thought of people as far as what their purposes were in my life. I paid no attention to Janie 37 she was a bus driver. I had 38 her by her job and brushed her off as unimportant.
For all I know, I’m

just another person in 39 else’s world, and may not be 40 . I should not have been so selfish and self-centered. Everyone has places to go, people to see and appointment to keep. Understanding people is an art.

C．conversation

D．disappointment

C．pessimistic

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