如图所示,AB是一质量为m的均匀细直杆,A端靠在光滑的竖直墙壁上,B端置于水平地

题型:选择题

问题:

如图所示,AB是一质量为m的均匀细直杆,A端靠在光滑的竖直墙壁上,B端置于水平地面上,杆身与竖直方向夹角为θ,杆与地面的摩擦系数为μ,保持平衡,则此时杆与地面的摩擦力为(  )

A.mgtgθ

B.mgsinθ

C.μmg

D.μmg

考点:摩擦力的大小摩擦力的种类杠杆的平衡条件
题型:选择题

阅读理解。

     Tom was three years old. He liked to watch TV with his parents after supper, but his parents never let

him stay long. Mother would say, "It's eight o'clock now. It's time for you to go to bed, Tom."

    "But why don't you go to bed, too?" Tom always asked.

    "We are adults (大人)," mother would say, "And adults go to bed late."

    One evening Tom asked his mother for an apple.

     "But it's too late," his mother didn't want to give him anything to eat at bedtime. "The apples are already

asleep."

     "But not all of them, Mom." Tom said, "The baby apples are perhaps asleep, but their parents are surely

awake."

1. Tom liked to watch TV with ________ after supper.

A. his father and mother

B. his sister

C. his grandparents

D. his brother

2. His parents ________ let him stay long.

A. never

B. sometimes

C. often

D. usually

3. One evening Tom asked his mother for ________.

A. an egg

B. an apple

C. an orange

D. a pear

4. His mother didn't want to give anything to him to eat ________.

A. in the morning

B. in the afternoon

C. at bedtime

D. at noon

5. From the story we know ________.

A. Tom was a quiet boy

B. Tom was a bad boy

C. Tom was a lazy boy

D. Tom was a clever boy

题型:选择题

()在一定温度下于含水的酸性介质中可发生脱磺水解反应,即磺化的逆反应

A.芳磺酸

B.浓硝酸

C.发烟硝酸,浓硫酸(并加热)

题型:选择题

决定流动资产周转天数的因素不包括()。

A.行业和技术特征

B.企业所处外部经济环境

C.管理流动资产周转的效率

D.新法规的出台

题型:选择题

放大电路中引入交流负反馈不能实现()。

A.展宽通频带

B.改变输入电阻

C.稳定放大倍数

D.提高放大器的增益

题型:选择题

()是人类迄今为止最科学的世界观和方法论。

A.马列主义

B.马克思主义哲学

C.“三个代表”精神

D.“八荣八耻”精神

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