物体做匀速圆周运动的半径为r,线速度大小为v,角速度为ω,周期为T,向心加速度为

题型:选择题

问题:

物体做匀速圆周运动的半径为r,线速度大小为v,角速度为ω,周期为T,向心加速度为a.关于这些物理量之间的关系,下列表达式中正确的是(  )

A.v=

ω
r

B.a=

ω2
r

C.ω=

2πr
T

D.a=

4π2r
T2

考点:线速度角速度
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为了除去粗盐中Ca2+、Mg2+、SO42-以及泥沙等杂质,某同学设计了一种制备精盐的实验方案,步骤如下:(用于沉淀的试剂稍过量)

(1)判断BaCl2已过量的方法是______;

(2)第④步中,相关的离子程式是______;

(3)若先用盐酸调PH再过滤,会对实验结果有影响吗?______(填“有”或“无”),试分析原因:______.

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阅读理解。

     There was a gardener who looked after his garden with great care.To water his flowers,he used

two buckets.One was a shiny and new bucket.The other was a very old and dilapidated one,which

 had seen many years of service,but was now past its best.

     Every morning,the gardener would fill up the two buckets.Then he would carry them along the

path,one on each side,to the flowerbeds.The new bucket was very proud of itself.It could carry a full

bucket of water without a single drop spilled (溢出).The old bucket felt very ashamed because of

its holes:before it reached the flowerbeds,much water had leaked along the path.

     Sometimes the new bucket would say,"See how capable I am!How good it is that the gardener

has me to water the flowers every day!I don't know why he still bothers with you.What a waste of

space you are!"

     And all that the old bucket could say was,"I know I'm not very useful,but I can only do my best.

I'm happy that the gardener still finds  a little bit of use in me,at least."

     One day,the gardener heard that kind of conversation.After watering the flowers as usual,he said,

"You both have done your work very well.Now I am going to carry you back.I want you to look

carefully along the path."

     Then the two buckets did so.All along the path,they noticed,on the side where the new bucket was

carried,there was just bare(光秃秃的) earth;on the other side where the old bucket was carried,

there was a joyous row of wild flowers,leading all the way to the garden.

1.What does the underlined word "dilapidated" probably mean?

A.   Dirty.  

B.   Dark.

C.Wornout.  

D.Plainlooking

2.What was the old bucket ashamed of?

A.   His past.  

B.His aging.

C.   His manner.  

D.His leaking.

3.The new bucket made conversations with the old one mainly to________.

A. laugh at the old one

B. take pity on the old one

C. show off its beautiful looks

D. praise the gardener's kindness

4.Why was the old bucket still kept by the gardener?

A. Because it was used to keep a balance.

B. Because it stayed in its best condition.

C. Because it was taken as a treasure.

D. Because it had its own function.

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借贷记账法的记账规则不包括______。

A.有借必有贷,借贷必相等

B.全部账户本期借方发生额合计=全部账户本期贷方发生额合计

C.全部账户期末借方余额合计=全部账户期末贷方余额合计

D.资产账户余额合计=负债账户余额合计

E.收入账户本期发生额合计=费用账户本期发生额合计

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DGS8800e数字调速系统,数字调节器(Regulator)的死区限值为±4RPM且恒定供油量控制模式模式没被激活,参数77设定值为2,那么则此时调节器的死区或不灵敏区为()。

A.±0.5RPM

B.±1RPM

C.±2RPM

D.±4RPM

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第一次国共合作形成的标志错误的是()。

A.1919年的“五四”运动

B.192年7月中共的成立

C.1924年1月中国国民党的“一大”

D.1926年7月9日国民革命军誓师典礼

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