Scholar’s Starry Sea

At this moment, Wu Bin is already sitting on the bus bound for Xianghai Middle School, which is the venue for this Physics competition.

There are a total of ten participating students on the bus, including Wu Bin. At this moment, Wu Bin, who is sitting alone with a book, is obviously a little isolated.

But this is normal. Among the other nine people, Zhang Qiu is the one who knows Wu Bin the most, but the best relationship between the two is to be classmates in the same class, oh , And they have been on duty together.

But Zhang Qiu and the other four senior high school students are old friends. They participated in the competition together from high school at first, and they have clenched their teeth all the way to the present. It is an absolute comradeship.

There are four remaining, two of them are freshmen in high school. It is estimated that they are going to practice military training, so they naturally sat together. The other two in high school can be considered to have initially established a comrade-in-arms relationship. They are talking now. What questions will be asked this time?

"Are you nervous?"

Seeing Wu Bin sitting alone, Bi Wanqing sat next to him and asked.

"Fortunately, the two teachers have so much confidence in me. I am still nervous." Wu Bin closed the book and replied.

Bi Wanqing laughed after listening: "Your logic is a bit reasonable, so have you completed the plan after the preliminaries?"

"Well, I will fight for I will fill up all other subjects within a week. Anyway, there is no problem with teachers in all subjects."

The study plan for Wu Bin has basically been arranged, according to his current progress. , It is not difficult to complete, and after passing this Physics competition, his experience is almost enough to upgrade, when the time comes, the new innate talent points can further improve his learning speed.

Of course, it would be more perfect if lottery could come again.

"Your self-confidence is really...like when I was young."

After speaking, both teachers and students laughed.

While the teachers and students were chatting, the bus quickly reached the destination and stopped at the door of Xianghai Middle School. After everyone got off the bus one after another, Bi Wanqing finally emphasized the competition and took it. The crowd entered the school.

Following the instructions of the staff, Wu Bin quickly found his own classroom, and by coincidence, Zhang Qiu was sitting not far away.

"Come on."

The two of them sat down after encouraging each other.

Next is to listen to the invigilator teacher to announce various examination room disciplines and issue papers.

As soon as the paper started, Wu Bin scanned the questions on the paper, and finally came to the conclusion.

'funny'

After scanning the question, Wu Bin can see that the questions on this paper are very polarized. Four of the five multiple-choice questions are "a little bit high school. People who are basic in Physics can answer it."

The first question is a Physics general knowledge question, the second question is a simple heat exchange of thermal studies, and the third question...Is this a Chinese question?

The fourth question, the test is light intensity, which is beyond the scope of high school. It is estimated that it is a bit difficult if you have not learned it, but if you have learned it, it is trivial.

The only difficult thing is the fifth question. Because the elliptical orbit brings some calculation difficulties and thinking difficulties, it is a bit tormenting, but it is okay for Wu Bin. For the brain problem, he has some troubles. After hard training, I'm pretty good at it.

Next is the fill-in-the-blank question, one is the simple harmonic vibration, using the classical model, it can be easily answered with the simple vibration mechanics equation.

The other two fill-in-the-blank tests are optics, a secondary optical axis and a Yang Clan double slit, both of which are basic knowledge in optics.

Up to this point, there are really no particularly exciting questions. Finally, it is a big question. The few questions are not too difficult to get started.

Among them, there are two electrical courses, one is the coil, which is the foundation of the basics, and the other is the calculation of the Hall coefficient. The type of the question is really not seen before, but it is not too difficult. , A few troublesome calculations can be done quickly with a calculator.

But the final mechanics question is really a sudden change in style, which is the most difficult question in the paper that Wu Bin thinks.

The title is like this.

An artificial satellite with a mass of m=3000kg moves circularly around Earth at a height of H=180km above the ground, where the gravitational acceleration g=9.3m·s minus 2 square due to air resistance In one year, the altitude of the artificial satellite will drop by ΔH=0.50km. It is known that the resistance F that an object receives when moving at a speed v in a fluid with a density of ρ can be expressed as F = 1/2 pACv², where A is the maximum cross-sectional area of ​​the object, and C is the drag coefficient, which is related to the shape of the object . When the satellite is operating at high altitude, it can be considered that the towing coefficient of the satellite is C=1, and the maximum cross-sectional area of ​​the satellite is A=6.0m². The radius of Earth is known to be R0=6400km. Try to estimate the atmospheric density where the satellite is located from the above data.

This is a final question about Gravity. It is natural to use the data given in the question to estimate the atmospheric density around the satellite.

This question can actually be regarded as hitting Wu Bin’s gun. The difficulty of this question Wu Bin sees is that the examinee needs to find the correct salient elements, ignore the secondary factors, and proceed. A reasonable estimate is the ability to read questions, which is the battlefield where abstract thinking ability can exert the greatest energy!

And what does this prominent element refer to?

Because the question design requires estimation of the atmospheric density where the satellite is located, it is known from F=12pACv² that p is required.

That is to find the relationship between F and v, so it is obvious that this is a problem of functional transformation.

After understanding the idea of ​​the question, it will be easy, the formula! That's it!

Solution: Suppose the speed of the satellite before and after 1 is v1 and v2 respectively. According to Gravity's law and Newton's law, there are

Mm of GR1²=v1² of R1, (R1=R0＋H )(1)

Mm of GR2²=v2² of mR2 (R2=R0+H-ΔH) (2)

The idea is there, the formula is listed, and the rest Just push, but there is a lot of mechanics knowledge involved, and the process is not easy.

Wu Bin let out a sigh of relief after the solution.

'Your sister, there are so many pits, Calculus has not learned it or it is hard, otherwise the force F in the question is a variable force, which can be solved by Calculus. '

' But it may also be a pit, anyway I can solve it. '

After relaxing, Wu Bin looked around and found that the classroom that was full of dangdang had already left a lot of people.

'Damn? ? ? The contestants are so scary? This topic is quite difficult, do you do it so quickly one by one? This means that the preliminaries are not difficult for them? '

'It seems that experts are gathered in the rematch. '

After thinking about Wu Bin, he looked towards Zhang Qiu's direction, and found that he was still there, and he kept scratching his head with his pen, looking uncomfortable.

'I guess I have solved the last question, Amitabha, come on. '

Wu Bin originally thought about handing in the paper, but when I thought that I was not putting pressure on Zhang Qiu this morning, I didn’t think about it. The method to solve two electrical problems is ready.