宇航员在月球表面附近高h处释放一个物体，经时间t后落回月球表面，月球半径为R．在月球表面附近绕月球做匀速圆周运动的宇宙飞船速率为

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宇航员在月球表面附近高h处释放一个物体，经时间t后落回月球表面，月球半径为R．在月球表面附近绕月球做匀速圆周运动的宇宙飞船速率为（）

A：2 $\frac{\sqrt{R h}}{t}$

B： $\frac{\sqrt{R h}}{t}$

C： $\frac{\sqrt{2 R h}}{t}$

D： $\sqrt{\frac{R h}{2 t}}$

上一题下一题 0.0难度选择题更新时间:2016-05-06 12:27:12

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C

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阅读短文，从A—E五个句子中选择正确选项还原到文中，使短文内容完整正确。

There are two days we shouldn't worry about in our life. One is yesterday,____ Yesterday is gone forever.____ So it is useless to worry about it. We cannot control tomorrow.____ maybe something good or bad. No matter tomorrow is sunny or cloudy, the sun will rise as usual. So we have only one day left. What is it?____Today is the most important for everyone. It is the only day for us to fight for ourselves. We can control it. We can choose what to do and what not to do. We can choose how to do it. Treasure Today,____

A. We cannot change what you said or what you did yesterday

B. We don't know what will happened next day

C. Yes ,it is Today

D. because it is our wealth our hand

E and the other one is tomorrow

选项	需区分的物质	方法一	方法二
A	碳酸钠溶液和碳酸氢钠溶液	加入酚酞试液	加入稀盐酸
B	浓盐酸和浓硫酸	打开瓶盖观察	滴在纸上观察
C	石灰水与氢氧化钠溶液	通入二氧化碳气体	加入紫色石蕊溶液
D	生石灰和熟石灰	加水观察	加水后分别加入酚酞试液

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