问题 选择题

如图所示,一人向右匀速推动水平桌面上的长木板,木板露出桌面后,在木板翻离桌面以前,则(  )

A.木板对桌面的压力将减小

B.桌面对木板摩擦力将减小

C.推力将逐渐减小

D.推力、压力、摩擦力均不变

答案

由图分析可知,当课本在桌面上匀速滑动时,压力不变,接触面的粗糙程度不变,只是接触的面积在逐渐减小,而我们知道接触面积的大小不影响摩擦力的大小,因此,摩擦力是不变的;

同时读图可知,课本在滑动的过程中,对桌面的压力不变.综合上述分析,只有选项D符合题意.

故选D.

单项选择题
阅读理解

阅读理解。

     Tess, eight, always heard her parents talking about her brother, Andrew. He was very sick and they were

completely out of money. Only a very costly surgery could save him but no one would lend them money. She

heard Daddy said with desperation, "Only a miracle can save him."

     Counting all her coins in her bedroom and carefully bringing the coins, Tess slipped out the door and made

her way six blocks to Drug Store. She waited patiently for the pharmacist (药剂师) to give her some attention

but he was too busy at this moment. Tess twisted her feet to make a noise. Nothing. She cleared her throat

with the most disgusting sound she could produce. No good. Finally she took a coin and banged (发出砰声)

it on the counter. That did it! "And what do you want?" the pharmacist asked. "I'm talking to my brother from

Chicago whom I haven't seen for ages," he said without waiting for a reply to his question. "Well, let's talk

about my brother," Tess answered. "He's really, really sick and I want to buy a miracle." 

     ''Pardon?" said the pharmacist, "Andrew has something bad growing inside his head and my Daddy says

only a miracle can save him now. So how much does a miracle cost?" "No miracle here." the pharmacist said.

"Please, just tell me how much it costs." Tess pleaded. The pharmacist's brother bent down and asked, "What

kind of a miracle does your brother need?". "I don't know," Tess replied. "Ijust know he's really'sick and

Mommy says he needs an operation." "How much do you have?" asked the man from Chicago. "One dollar and

eleven cents." Tess answered shyly. "Well, what a coincidence (巧合)!" smiled the man, "That's the exact price.

Take me to where you live. Let's see if I have the kind of miracle you need."

     That man was Mr. Carlton. The operation was completed without charge and soon Andrew was home again 

     "That surgery," her Mom whispered, "was a real miracle. I wonder how much it would have cost?" Tess

smiled. She knew exactly how much a miracle cost.

1. According to the passage, which of the following statements is TRUE? [ ]

A. A miracle costs one point eleven dollars plus the faith of a little child.

B. Tess tried once to get the attention from the pharmacist but failed.

C. Tess's brother, Andrew, didn't survive the operation.

D. Tess is very brave to walk 5 blocks to the drug store to get help.

2. From the passage, you may see Mr. Carlton is _____. [ ]

A. a pharmacist

B. a policeman

C. a teacher

D. a surgeon

3. What was the pharmacist's attitude towards the girl when she tried to get his attention? [ ]

A. delighted

B. impatient

C. nervous

D. anxious

4. Which of the following proverbs best describes what happened in the story? [ ]

A. Nothing is impossible to a willing heart.

B. Two heads are better than one.

C. The early bird catches the worm.

D. Behind bad luck comes good luck.