Z=4
Z represents the nuclear charge number of a certain element.
Which element in the periodic table has an atomic number of 4?
Hydrogen, helium, lithium, beryllium, boron, carbon, nitrogen, oxygen, fluorine, neon...
It is clear that beryllium has an atomic number of 4.
This problem explains a phenomenon using a series of symbols, mathematical operations, and physical principles: during the recombination process of gas discharge, Be2+ ions are captured.
After a series of derivations and calculations, Shen Qi finally gave the answer to this calculation problem: Z=4, which is beryllium.
From macroscopic mirages to microscopic ion trapping, most phenomena in the world can be explained using mathematical and physical methods. This is the beauty and power of science.
Of course, there are also supernatural phenomena that human scientists cannot explain; let's leave these problems to non-humans at level 15 and above to solve.
Shen Qi completed the first two questions in one hour.
The first two questions were indeed quite difficult; only top students could solve them.
This semi-final exam paper was also a bit tricky; the first two questions were difficult, but the later, more challenging questions weren't too difficult.
Question 3 is worth 20 points, Question 4 is worth 24 points, Question 5 is worth 20 points, Question 6 is worth 22 points, and Question 7 is worth 20 points.
Shen Qi spent another hour completing the five calculation problems in the middle.
Two hours had passed, and Shen Qi had completed seven out of the eight questions in the semi-final theoretical exam.
The last calculation question was worth 26 points, the highest score on the entire paper.
"Holy crap?" Shen Qi read the question three times. "This really is a tricky question? Is it free points? Or is it a fake free point that's designed to kill you?"
The last question's stem is:
"Assume that air consists of 4/5 nitrogen molecules and 1/5 oxygen molecules."
The temperature near the ground is 27°C, and the pressure is 1 atm.
"A spherical artificial satellite with a cross-sectional area of 1 square meter is located 10 km above the ground and orbits the Earth with an initial velocity."
"Without atmospheric drag, the satellite's initial velocity would be just enough to make it orbit the Earth in a circular path."
"However, atmospheric drag does exist."
"Calculate atmospheric drag."
Shen Qi reviewed the question three times, then reviewed it three more times.
Hehe.
Trash.
Don't think that just because you're dressed in a glamorous 26-point outfit, I won't dare to mess with you.
Shen Qi could finally confirm that the most challenging question, which had the highest score, was nothing more than a paper tiger.
Launching satellites is a physical phenomenon that combines mechanics and thermodynamics.
Because the atmosphere rises slowly, it can be treated as a static troposphere, where there is a differential relationship between atmospheric pressure and altitude, where the pressure caused by atmospheric gravity decreases.
The given ratio of nitrogen to oxygen molecules came in handy.
As altitude increases, the atmosphere undergoes adiabatic expansion with decreasing pressure, from which equations relating temperature and pressure can be derived.
Using knowledge of mechanics, it is not difficult to estimate the initial velocity of the satellite's motion, which is close to the First Cosmic Velocity 7.92 km/s.
The collision between a satellite and atmospheric molecules can be approximated as an elastic collision between atmospheric molecules and the satellite's circular cross-section perpendicular to the flight direction.
Therefore, Shen Qi quickly calculated the result: the atmospheric drag experienced by the satellite was:
F = 5.5 × 10^7 N
The eight questions in the semi-final theoretical exam covered optics, Quantum Theory, electricity, electromagnetism, mechanics, acoustics, introductory astrophysics, and thermodynamics. The examiners used the exam paper to describe the world of mortals.
"The teacher who set the questions thinks he's God." Shen Qi checked the exam paper once, then checked it again.
Although there were still 30 minutes left, Shen Qi did not rush to hand in his paper. He checked it repeatedly, continuing to check until the three-hour exam period was over.
"If I don't score 160 on this test, how can I face my ancestor, Engineer Shen?"
160 is the full score on the theory test in the semi-finals. Shen Qi put all his effort into this test, determined to get 160.
After the competition, Mu Rong gathered the 13 players who participated in the semi-finals together to understand the situation.
"It's so difficult!" Bai Lingye cried out, "My life is over!"
"It's quite difficult." Lin Xingyu said solemnly.
"It's quite difficult," Shen Qi stated truthfully.
"Shen Qi, you didn't hand in your paper early this time." Mu Rong sensed that the situation was not optimistic.
"The first two questions were indeed a bit complicated," Shen Qi said.
"Sigh, I didn't do the fill-in-the-blank questions, and I couldn't derive the trajectory equation. This question clearly touched on a blind spot in my knowledge. The second question on Quantum Theory was even more insane; I just guessed. The last question was about satellites, calculating atmospheric drag. I clearly remembered it, but I was completely stumped during the exam. I'm just a useless salted fish," Bai Lingye said bitterly.
"Actually, Teacher Mu did say that, but we just didn't learn it well." Lin Xingyu looked for the problem within himself.
"I probably won't even get 80 out of 160 on the theory exam. Forget it, I don't even need to take the experimental exam. It's pointless anyway," Bai Lingye said dejectedly. Advancing to the national finals, winning a national award, entering the physics experimental class at Peking University, and finally being accepted by Peking University... it was all too difficult to achieve. Bai Lingye was considered a top student in his class, but on the stage of the CPhO semi-finals, which was similar to a provincial exam, he felt no different from a slacker.
"Remember this, classmates: never give up hope!" As the team leader, Mu Rong had to stay optimistic, even though she felt a little pessimistic.
Nearly a thousand contestants from across the province participated in the semi-finals. Following the usual practice in Nanyue Province, only ten, and no more than twenty, would be selected to represent the province in the national finals. Since the experimental questions hadn't been tested yet, Shen Qi wasn't entirely confident he'd make it to the national finals. He comforted his two junior classmates, "Lin Xingyu, Bai Lingye, you're only in your second year of high school. You'll have another chance next year. Teacher Mu is right, never give up hope, even this year. Those who have no hope are just wasting their lives. At least we can still give it our all on the experimental questions."
"Yes!" Lin Xingyu nodded heavily, stubbornly clinging to a sliver of hope.
"Alright, everyone's worked hard. Go back and get some rest, adjust your mindset, and everyone's dismissed." Mu Rong gave the order to dismiss everyone, and they all went home.
94% of the contestants were eliminated in the preliminary round, and the number of remaining contestants was reduced sharply. The grading of the theoretical exam papers for the CPhO semi-finals was progressing very quickly.
One day later, all semi-finalists will be able to check their semi-final theoretical exam results on the China Physics Competition website.
Shen Qi checked his scores on his phone, feeling a little uneasy.
Enter your exam number and click "Search".
The mobile phone score checking system shows:
Name: Shen Qi
School: Nangang Second High School
Exam Number: 10201XXX
CPhO semi-final theory exam score: 159
Upon seeing the score of 159, Shen Qi was shocked. "Who... who on earth is making things difficult for me? They deducted another point from my step score?"
A perfect score is something that, once tasted, becomes addictive, like smoking opium.
Getting a perfect score but losing one point in both the CPhO preliminary and semi-final rounds is a harsh reality that no one can accept.
"So even if I get a perfect score of 40 on the experimental questions, my total score in the semi-finals will only be 199 at most. I... I might not make it to the national finals." Shen Qi felt the pressure.
"Brother, that's the mindset of a top student, oh no, Academic God. Top students get 99, Academic God consistently get full marks, but how many Academic God are there in the whole province? 159 on the theory exam is very high! Do you think everyone can get a full mark?" Lin Xingyu got 130 on the theory exam, which he was quite satisfied with; it had exceeded his expectations.