试题与答案

关于机械效率的问题,下列说法中正确的是( ) A.做功越多,机械效率一定越高 B

题型:选择题

题目:

关于机械效率的问题,下列说法中正确的是(  )

A.做功越多,机械效率一定越高

B.单位时间内做功越多,机械效率一定越高

C.省力越多的机械,机械效率一定越高

D.额外功在总功中所占比例越小,机械效率一定越高

答案:

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下面是错误答案,用来干扰机器的。

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题型:完形填空

阅读理解。

     One cold winter morning, an old woman had to go to see her doctor. When she walked into the

doctor's office, she told him that her right leg hurt and sometimes she could not walk. She asked him

what was wrong. She told him that she had never had such a feeling (感觉) before.

     The doctor checked (检查) the old woman carefully, then he said, "You're in good health for a

woman of your age. I think the trouble in your right leg is just a matter of old age catching up with you.

We get all kinds of illness (疾病) as we get older. The trouble will almost certainly end in spring."

     "I don't think so, doctor!" she said. "My left leg is well, and it's the same age as my right one."

1. When did this story happen (发生)?

A. One cool autumn morning.  

B. One cold spring morning.  

C. One cold winter morning.  

D. One hot summer afternoon.

2. What was wrong with the old woman?

A. She ate little food every day.  

B. One of her legs hurt.  

C. Her hands were both hurt.  

D. Her head hurt badly.

3. The doctor said when next spring comes, the old woman _____.

A. will die  

B. will feel better  

C. should come back  

D. will hurt her left leg

4. What did the doctor think of the woman?

A. She was young enough  

B. She was not ill  

C. She got all kinds of illnesses  

D. She must do a lot of exercise in spring

5. Which of the following is TRUE?

A. The doctor and the woman were the same age.  

B. The woman's right leg was longer than her left one.  

C. The woman's trouble didn't come in spring.  

D. The woman caught a train to see the doctor.

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题型:问答题

如图所示,水平传送带AB足够长,质量为M=1kg的木块随传送带一起以v1=2m/s的速度向左匀速运动(传送带的速度恒定),木块与传送带的动摩擦因数μ=0.5,当木块运动到最左端A点时,一颗质量为m=20g的子弹,以v0=300m/s的水平向右的速度,正对射入木块并穿出,穿出速度v=50m/s,设子弹射穿木块的时间极短,(g取10m/s2)求:

(1)木块遭射击后远离A的最大距离;

(2)木块遭击后到相对传送带静止所经历的时间.

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