问题 多选题

搭载着嫦娥二号卫星的长征三号丙运载火箭在西昌卫星发射中心点火发射,卫星由地面发射后,进入地月转移轨道,经多次变轨最终进入距离月球表面100公里,周期为118分钟的工作轨道,开始对月球进行探测(  )

A.卫星在轨道 III上的运动速度比月球的第一宇宙速度小

B.卫星在轨道 III上经过P点的速度比在轨道 I上经过P点时大

C.卫星在轨道 III上经过P点的向心加速度比在轨道 I上经过P点时小

D.卫星在轨道 I上的机械能比在轨道 II上大

答案

A.月球的第一宇宙速度是卫星贴近月球表面做匀速圆周运动的速度,卫星在轨道Ⅲ上的半径大于月球半径,根据

G

Mm
r2
=m
v2
r
,得v=
GM
r
,可知卫星在轨道Ⅲ上的运动速度比月球的第一宇宙速度小.故A对.

   B.卫星在轨道Ⅰ上经过P点若要进入轨道Ⅲ,需减速.故B错.

   C.卫星在轨道Ⅱ上和在轨道Ⅰ上经过P时所受万有引力相等,所以加速度也相等,故C错.

   D.卫星从轨道Ⅰ进入轨道Ⅱ,在P点需减速.动能减小,而它们在各自的轨道上机械能守恒,所以卫星在轨道Ⅰ上的机械能比在轨道Ⅱ上多.故D对.

故选AD.

默写题
完形填空
Nowadays more and more Chinese teenagers find life more difficult without their parents. They don’t know how to do       . Because their parents do almost __   for them at home . This is a big __ __.
Joy is 14 years old. One day her __ __ went away       business, so she had to stay at __ __alone. At first she thought she would be happy       her parents were not in. She could do everything      she liked. But it was six o’clock in the afternoon, she felt    . “Oh, it’s time to have __ __. Where can I get my __ _?” she said to _ __. Later she found some food in the fridge, but she       know how to cook. At that moment, she missed her       very much. At last she could only go to the supermarket and       some food to __ __.
Many__ _ are      as Joy. So I think they should learn some basic _ _ skills, like cooking, tidying up their rooms or dressing themselves      . They shouldn’t depend too much on their parents.
小题1:
A.homework B.houseworkC.businessD.some shopping
小题2:
A.nothing B.somethingC.everythingD.some
小题3:
A.question B.quarrelC.fightD.problem
小题4:
A.parents B.uncleC.aunt D.brother
小题5:
A.in B.atC.with D.on
小题6:
A.schoolB.churchC.hospitalD.home
小题7:
A.becauseB.soC.butD.until
小题8:
A.whenB.whoC.where D.that
小题9:
A.fullB.hungryC.excitedD.bored
小题10:
A.supperB.breakfastC.lunchD.brunch
小题11:
A.bookB.orangeC.drinkD.food
小题12:
A.herselfB.himselfC.myself D.themselves
小题13:
A.couldn’t B.didn’tC.might not D.wouldn’t
小题14:
A.cousinB.auntC.parentsD.brother
小题15:
A.madeB.gaveC.bought D.saw
小题16:
A.drinkB.eatC.make D.give
小题17:
A.menB.womenC.adults D.teenagers
小题18:
A.the same B.difficult C.differentD.warm-hearted
小题19:
A.schoolB.studyC.life D.play
小题20:
A.properlyB.carelesslyC.actuallyD.Slowly