Fang Chao answered quickly, and in just a while, he had already completed the fourth question in the second part.

4 (10 points) In the winter in northern China, even if the temperature is very low, the water in some deep rivers, streams, lakes and ponds will generally not freeze to the end, and fish can also spend the winter safely when the water surface is frozen, try to explain the reason why the water will not freeze to the end.

In the case of physics competitions, most of the questions are common types of questions in life, which does not require a huge amount of calculations like mathematics, and even requires you to draw a lot of auxiliary lines, etc., so some prestigious schools recruit students to prefer to be people who have excellent results and performance in io competitions, because their thinking is more groundbreaking.

Of course, this does not mean that the physics competition is unattended, some outstanding students will still be recognized by prestigious schools, and there are also some admissions offices of famous schools who come here to step on the spot, wanting to tap excellent physics geniuses.

Fang Chao quickly finished writing most of the fourth question.

In autumn and winter, the temperature begins to drop, the water layer in the river, lake, pond first becomes colder, the density becomes larger and sinks to the bottom of the water, forming convection, if the temperature decreases again when it reaches 4C, the upper water expands, the density becomes smaller, the convection stops, 'floats' on the water surface, forming a 'cover', and the water below mainly relies on heat conduction and loses internal energy, but because the water is a poor conductor of heat, so the heat dissipation is relatively slow.

The temperature of the surface water drops to 0C before the water below and begins to freeze, the density of the ice is smaller than that of water, so it floats on the surface of the water without sinking, and the water under the ice, the temperature from top to bottom is 0C to 4C, and if it cools down again, it will gradually freeze from top to bottom.

As long as the temperature is not too low or the low temperature is not long, and the water in the lake and pond is deep, the water will not be frozen, and the ice will not be frozen to the bottom.

The type of physics itself does not require a large amount of data to realize, it is more reflected in the bits and pieces of life, not as complex as mathematics, as long as you know the various changes in it, then it is easy to answer.

Fang Chao's level of physics is lv3, which makes him face some advanced levels such as quantum mechanics and electromagnetism, but just common common sense in life, then he is definitely capable of easily dealing with it.

"Tsk, the four questions of the short-answer questions are not too difficult, and then I will send you a fifth question, which is not a score anyway, but it always feels uncomfortable to be empty, even if I get the first place, someone is on a par with me, but people have done all the extra questions, but I am empty, so this first place is somewhat unworthy of the name."

"Harm ......"

The heart of defense is indispensable.

Fang Chao was on guard, and he knew that there were really very few people as perverted as him in this world, and besides, it only took him twenty-three minutes to get the first part and the second part, and the rest was only the final third part.

Fang Chao, who had completed the two major parts, glanced up at the people on his side and behind him, and found that most of them were immersed in contemplation, and some of them were turning their pens over there, as if they were stuck in a problem.

"Is there a problem here?"

Fang Chao was stunned for a moment, shouldn't it, these are simple basic operations, aren't they?

Even he was a little skeptical that the big guy who asked the question this year had specially opened the back door for the candidates, but it shouldn't be......

An invigilator stared at Fang Chao for a while when he saw Fang Chao's 'thief's head and brain', and said in his heart, are you still thinking about cheating at this time?

So he staggered to Fang Chao's vicinity, wanting to see how far this student had accomplished, if he had only done a few multiple-choice questions, but when his eyes fell on Fang Chao's physics test paper, he couldn't help but be stunned for a moment.

Do all the multiple-choice questions?

So fast?

Blind, right?

Don't you have to calculate?

Although some physics questions are easy to solve, there are also some questions that require a small range of calculations to arrive at the correct answer, and there is not even a draft on the other party's test paper, which really makes the invigilator very suspicious.

His gaze swept quickly over some of the questions on the multiple-choice questions, but the suspicion on his face was even stronger.

Copied?

Because he found that there were no mistakes in the multiple-choice questions he was looking at, and if he was a multiple-choice question, he also screened out all the correct answers, and the answers to the multiple-choice questions he knew, none of the other party's questions were wrong.

It shouldn't be.

I'll look at the short-answer questions again.

His gaze once again fell on the second part of Fang Chao's physics volume.

When he saw this, he was shocked again.

What?

Five short-answer questions?

You've answered all the damn things? And the answers written in each question are so difficult to find fault with the questions.

I have nothing to say if you only answer four questions, but you have already answered all four questions, and now you don't even let go of the fifth question? You want to answer all the questions in the test paper......

What the hell!

Feelings: You just looked around because you were tired of handwriting and wanted to relax?

Are you a pervert?

The invigilator has mixed feelings in his heart, and then look at the other contestants, many of them are still on the multiple-choice questions, even if some are fast, they are only the second question of the short-answer questions, but what about this contestant? He has already completed all five questions of the short-answer question.

People are more angry than people.

This player may be a dark horse in the physics competition.

After relaxing for about two minutes, Fang Chao quickly devoted himself to the third part of the physics competition.

For the same five questions, candidates only need to do four small questions, each of which is worth 15 points, for a total of 60 points.

If you choose the fourth question, the fifth question will not be counted in the total score, and if both questions are answered, the fourth question will be used as the topic for grading.

Title.

The air reservoir of the submarine is connected with the water tank, when the air in the air reservoir is pressed into the water tank, the water tank is discharged from the water, the submarine floats, the volume of a submarine gas reservoir is 23, the barometer on it shows that there is compressed air with a pressure of 2x10 to the seventh power PA inside, the compressed air in the cylinder is used to discharge the water tank with a volume of 103 water in the tank out of the water tank in the floating operation after a diving to the bottom of the operation, and the barometer shows that the pressure of the remaining air in the cylinder is 95x10 to the sixth power PA, Assuming that the temperature of the compressed air remains unchanged during the discharge process, the depth of the submarine is estimated at the seabed.

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