试题与答案

如图，重为200牛的重物由ON、OM绳悬挂在天花板上，已知ÐONM=60°，ÐO

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题型：填空题

题目：

如图，重为200牛的重物由ON、OM绳悬挂在天花板上，已知ÐONM=60°，ÐOMN=30°，请画出O点的受力分析图，绳ON受到的拉力是        N和绳OM受到的拉力是        N。

答案：

173N　　100N    受力分析如右图

题目分析：由图得到，，，.

点评：本题学生明确三个共点力平衡，任两个力的合力与第三个力是平衡力，用直角三角形的边角关系求解。

考点：共点力的平衡
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     Hi, there! I’m Crystal Collins, and I’m very happy to share some time with you. So, you want to keep

fit, huh? Well, you surely came to the right place. Together we can keep fit and healthy, and succeed in

doing that. It’s easy. Everybody can do it, you hear? Just remember the five golden rules.

     Number one. Always wear comfortable clothes when you are exercising. You need to feel comfortable and relaxed.

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real thing.

     Number three. Never try to do too much exercise too soon. Take it nice and easy now, you hear?

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     Number four. Don’t forget to relax for about five minutes when you’ve finished your exercise. You

need to rest a little bit after you’ve been exercising.

     And here is golden rule number five. Stop at once if you feel any pain in your neck, head or any part of your body.

1. Crystal Collins may most probably be _____.

A. a teacher

B. a doctor

C. a policeman

D. a scientist

2. Crystal Collins may most probably say this _____.

A. before the exercise starts

B. when the exercise is over

C. during the exercise

D. as soon as the exercise has started

3. What does the underlined words “Take it nice and easy” in Paragraph 4 mean?

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C. Have a good rest.D. don't exercise too tiredly .

4. Which of the following is NOT true about exercising?

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C. You should rest for a while when you are doing warming-up exercises.

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