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飞机从一地起飞，到另一地降落，如果在竖直方向上的分速度vy与时间t的关系如图所示（规定竖直向上为正方向），则飞机在飞行过程中上升的最大高度是______m；在t1=2200s到t2=2400s一段时间内，它在竖直方向上的分加速度ay为______m/s2．

答案

飞机在0-600s竖直方向的位移向上，在18-22s内竖直方向的位移向下，根据“面积”大小等于位移可知，在600s末飞机的高度最高，则h=

1
2
×20×(600+200)m=8000m，

由斜率等于加速度得到，在2200s--2400s内，飞机在竖直方向的加速度ay=

△vy
△t
=
0-(-20)
200
m/s2=0.1m/s2．

故答案为：8000，0.1；

单项选择题

《地面水环境质量标准》将水域划分为五类，其中( )适用于农业用水区及一般景观要求水域

A．Ⅰ类
B．Ⅱ类
C．Ⅲ类
D．Ⅳ类
E．Ⅴ类
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Questions


·Read the following passage and choose the best word for each space.
Do you want to send an e-mail message to the White House
Good luck.
In the past, (26) President Bush — or at least those assigned to read his mail — what was (27) your mind it was necessary only to sit down at a personal computer connected to the lnternet and (28) a note to president@ whitehouse.gov.
But this week, Tom Matzzie, an online organizer with the A.F.L.-C.I.O., discovered that (29) with the White House had become a bit more (30) . When Mr. Matzzie sent an e-mail protesting (31) a Bush administration policy, the message was bounced back With an automated reply, saying he had to send it again in a new way.
Under a system (32) on the White House Website (33) the first time last week, those who want to send a message to President Bush must now (34) as many as nine Web pages and (35) a detailed form that starts by asking whether the message sender supports White House policy (36) differs with it.
The white House says the new e-mail system is an effort to be more responsive (37) the public and offer the administration "real time" access (38) citizen comments.
Completing a message to the president also requires (39) a subject from the provided list, then entering a full name, organization, address and e-mail address. (40) the message is sent, the writer must wait for an automated response (41) his message, (42) whether the addressee intended to send the message. The message is delivered to the White House only after the person using that e-mail address (43) it.
"Over (44) , it’s a very cumbersome process," said Jakob Nielsen, an authority on Web design. "It’s probably designed deliberately to (45) on their e-mail.\

A. cut off B. see off C. dash off D. give off
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