初三问题(数理化英)

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查看11 | 回复5 | 2009-2-1 12:01:56 | 显示全部楼层 |阅读模式
一支长为130米的队伍做匀速直线运动,速度为5米/秒,方向与列车同向。列车长150米,以54千米/时的速度匀速前进。问列车要越过这列队伍,需多长时间?
“有人说4克镁条在1克氧气中点燃,完全燃烧后生成5克氧化镁,符合质量守恒定律。”这句话错在哪里?
大气中含量最多的元素是什么?
以下各组物质都属于混合物的是()
(A)海水和蒸馏水
(B)液氧和天然气
(C)碘酒和纯盐酸
(D)胆矾和空气
(E)煤和石油
(F)食醋和牛奶
已知P是正方形ABCD内一点,且点P到ABC三个顶点的距离分别为1、2、3,求这个正方形的面积。
翻译句子:
I rarely buy a morning paper.
He is the Newton of this age.
The robber and murderer was killed.
The earth turns itself from west to east.
Bob has a deep love for the Chinese art.
The public showed great interest in Russian films.
Is there any flower on the table?
We had supper at the Greens and we liked the dinner very much.
We have many subjects at school. i like Chinese, maths and English best.
Do you know this is a one-way street?
If I fail this time, I'll try it a second time.
One rainy day, a friend of mine came to see me.
We are going to have a party on New Year's Eve.
We pay the rent by the month.
people asked.
First someone took picture of the bridge.
The tenth five-year plan is now being carried out.
I will wait for you at the school gate at two o'clock this afternoon.
What's the population of China? It's about 1,300 million.
There aren't any better 200-metre runners than him in our school.
Eighty percents of the population of our country are farners.
China has an area of 9.6 million square kilometres.
He has traveled three-fourths of Beijing.
Will you take Bus No.13 or the No.18 bus?
Do you know what a quarter to eight is? It's fifteen to eight.
Shortly after the accident, two dozen policemen were sent to hte spot to keep order.
Thursday is the fifth day of the week.
He is staying in Room 201.
(都要有过程!)
更正一下Shortly after the accident, two dozen policemen were sent to hte spot to keep order. 中的hte应该是the,打太快了~~
呃,第一题的确就是这样的。标答上写:28秒。(天知道这个答案怎么来的)
正方形面积的那一题,标答上写:5+2√2(还是不知道这个答案怎么来的。要注意哦,点A、P、C不一定同线)

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千问 | 2009-2-1 12:01:56 | 显示全部楼层
第一道题不会。“有人说4克镁条在1克氧气中点燃,完全燃烧后生成5克氧化镁,符合质量守恒定律。”这句话错在哪里? 根据质量守恒定律,2Mg + O2 ===2MgO
48
32
80镁和氧气和氧化镁的质量比为48:32:80=3:2:5所以只有3份质量的镁和2份质量的氧气反应才能生成5份质量的氧化镁。故错误-------------------------------大气中含量最多的元素是什么? 氮气(氮气78%,氧气21%,稀有气体0.94%,二氧化碳0.03%,其他气体和杂质0.03%)-----------------------...
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千问 | 2009-2-1 12:01:56 | 显示全部楼层
1.这一道是不是缺条件,题目打全了吗? 可能是150/(54*5/18-5)=15s 2.质量守恒定律是指参加反应的各物质的质量总和等于生成的各物质的质量总和。1g氧气只能和0.75g镁完全反应,生成1.75g氧化镁,说法错误,有3.25g镁没有反应。 3.O 4.cef (A)海水是混合物,蒸馏水是纯净物 (B)液氧是液态氧气,属于...
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千问 | 2009-2-1 12:01:56 | 显示全部楼层
1)设需要X秒,54千米/时=15米/秒5X+130+150=15XX=282)4份镁完全燃烧需要多于一份的氧气3)氮气78%,氧气21%,稀有气体0.94%,二氧化碳0.03%,其他气体和杂质0.03%) 4)以下各组物质都属于混合物的是(EF) (A)海水和蒸馏水 (蒸馏水是纯净物) (B)液氧和天然气 (液氧是是纯净物) ...
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千问 | 2009-2-1 12:01:56 | 显示全部楼层
以下内容如果看不懂,或还有疑问,请联系hi.baidu.com/sf345505317第一题:题目不全,没说明初始时,列车与队伍的关系。但思路都一样:假设队伍是静止的,那么列车的速度是10m/s 第二题:不是生成“氧化镁”的质量为5g,是“燃烧后的总产物”质量为5g 第三题:氮(N) 第四题:帮你分析一下 (A)海...
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千问 | 2009-2-1 12:01:56 | 显示全部楼层
我来回答第一题,其它已经回答得很好了,我就不再回答了:
设它们同时行了X秒。
54千米/小时先化成15米/秒
130+5X = 15X-150
-10X = -280
10X = 280
X = 28x = 28 就这样得来的,我也是初三的,有问题大家想。...
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