地球质量约为月球质量的81倍，在登月飞船通过月地之间引力F地船=

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问题选择题

地球质量约为月球质量的81倍，在登月飞船通过月地之间引力F_地船=F_月船的位置时，飞船离月球中心和地球中心的距离比为（）



A．1∶27

B．1∶9

C．1∶3

D．3∶1

答案

B

设飞船质量为m，当F_地船=F_月船时，飞船距地球中心的距离为r₁,距月球中心的距离为r₂,根据万有引力定律和题意有.

选择题

( ) 1.	A. What does your mother do? She is a TV reporter. B. What does your father do? He is a policeman.
( ) 2.	A. How does she go to work? She goes to work on foot. B. How does he go to school? He goes to school by bike.
( ) 3.	A. Where does your aunt work? In the hospital. B. Where does your uncle work? In the cinema.
( ) 4.	A. She teaches Chinese. She is a Chinese teacher. B. She likes drawing pictures. She is an artist.
( ) 5.	A. I like playing the violin. B. I like collecting stamps.

单项选择题 A1型题

脊髓亚急性联合变性可出现精神症状的原因为

A．大脑白质受累

B．大脑灰质受累

C．脑干受累

D．周围神经受累

E．以上均不正确