航天员乘坐航天飞机去修理位于离地球表面h的圆形轨道上的哈勃太空望远镜片，航天飞机s进入与望远镜H相同的轨道并关闭助推火箭，而望远镜则在航天飞机前方数千米处，如图所示。设G为引力常数，M为地球质量，R为地球半径，V1为第一宇宙速度。
（1）在如图所示的航天飞机s内，质量m=70 kg的航天员的视重是多少？
（2）计算航天飞机在轨道上的速率和周期；
（3）航天飞机必须先进入半径较小的轨道，才有较大的速率追上望远镜。试判断航天飞机要进入较低轨道时应在原轨道上加速还是减速？说明理由。
解：（1）由于完全失重，视重为0N
（2）对近地卫星有：
①
对航天飞机有：
②
解方程①、②得：
由
，得：
（3）减速，当
时做近心运动
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| Nowadays green food is popular. We know we need green food and good health, 1 not all people knew that years ago. When I was in Grade 8, my teacher asked us to 2 something about green food by ourselves. We didn't have any idea at first. Then our four-member group had a 3 and decided to do some research in a supermarket. Two of us wrote down the names of the 4 food on the shelves. The other two asked 5 some questions like "Do you know what green food is?" "How often do you 6 green food?" and so on. More than 30 customers 7 our questions! Later each group in our class wrote a research report 8 the topic and handed it in. Our teacher chose the 9 ones and put them up on the wall of the classroom. 10 was among them! We not only learned a lot about green food but also knew how to keep healthy. | |||
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