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问题 选择题

某人在高h处抛出一个质量为m 的物体，不计空气阻力，物体落地时速度为v，该人对物体所做的功为（　　）

A．mgh

B．

mv2
2

C．mgh+

mv2
2

D．

mv2
2-mgh

答案

人对小球做的功等于小球获得的初动能，

根据对抛出到落地的过程运用动能定理得：

mgh=

1
2
mv2-
1
2
mv02

解得：

1
2
mv02=
1
2
mv2-mgh

即人对小球做的功等于

1
2
mv2-mgh

故选D

单项选择题

饮片外表面较为粗糙，呈鳞片状剥落的药材为

A．川木通
B．秦皮
C．石菖蒲
D．苦参
E．百部
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填空题

根据句意和音标提示写单词。

1. Sun Haiping is Liu Xiang's ___________/ k?ut /.

2. My parents always ___________/  / me when I haven't got good marks.

3. Liu Xiang broke the world ___________/'rek:d / with a time of 12.88 seconds in 2006. Now he is

still the holder(保持者).

4. Every Chinese hopes Liu Xiang will get a new gold ___________/'medl / at the Beijing Olympics.

5. Jim was chosen to ___________/'ri:pri'zent / the students' union to attend the meeting.

6. We should go to bed and get up ___________ /'regju:l?li / every day.
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