在“探究求合力的方法”的实验中,王同学用了两个量程为5N、最小刻度为0.1N的弹

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问题:

在“探究求合力的方法”的实验中,王同学用了两个量程为5N、最小刻度为0.1N的弹簧秤来测量拉力.实验之前他先检查了弹簧秤,然后进行实验:

(1)实验前对弹簧秤进行检查,下列哪些检查是必需的?______.

A.将弹簧秤放在桌面上,进行调零

B.将弹簧秤竖直放置,进行调零

C.将弹簧秤用力拉,看是否能达到最大量程

D.将两只弹簧秤水平互钩对拉,检查两弹簧秤读数是否相同

(2)实验情况如图甲所示,其中A为固定橡皮筋的图钉,O为橡皮筋与细绳的结点,OB和OC为细绳.图乙是在白纸上根据实验结果画出的图.图乙中的F与F′两力中,方向一定沿AO方向的是______;本实验采用的科学方法是______(填“理想实验法”、“等效替代法”或“控制变量法”).

考点:实验:验证力的平行四边形定则
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安全电子交易系统模型中的核心机构是()。

A.发卡行

B.商家

C.商业银行

D.认证中心

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工作坑的作用是什么?

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F1动物有何优点?

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B Egyptian Villages 埃及村落

Most of the inhabitants live in mud-brick homes, their (1)  walls insulating against the afternoon heat. Flat roofs, exposed (2)  the northern evening breezes, serve as cool sleeping (3)  as well as storage areas. Villagers plaster the outer walls (4)  often trim them in blue, a color they believe (5)  off the evil eye. As a man becomes richer, (6)  can add a second story to his house perhaps (7)  his married son. Those villagers who have made the (8)  to Mecca paint the legend of their trip on (9)  outer walls of their homes. Such hajj houses, along (10)  the mosques, are the most distinguished buildings in a (11)

Some villagers build ornate pigeon coops close to their (12) , using the birds as food and their droppings to (13)  crops. Many houses still have dirt floors and lack (14)  or running water; women with jars balanced on their (15)  make the trek to the community well, and children donkeys haul the (16)  liquid in jerry cans.

All (17)  said, government sponsored building programs have also brought newer (18)  residences and utilities to some villages, particularly those outside (19)  Nile Valley in the Oases and the Red Sea (20)  areas.

4.()

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简述电视传播的优势和劣势?

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