Chapter 10: The Past Is Unbearable

Now that the self-study class is halfway there, everyone is borrowing homework just now, and it is very lively. However, it seemed that I was the only one who did the last question, so most of the students in the classroom asked me to borrow my homework to copy. But it's quiet now, and Wenbo's table with me is stuffed with snacks.

"Zhou Yu, this ......"

Zhang Guihua suddenly turned her head and handed me an Alpine lollipop on my desk. Then she hesitated and said, "Can you ......?"

I understood as soon as I saw that she also wanted to copy her homework. But when I didn't understand English, I had to ask her questions, and now she asks me to copy my homework, which is helping each other. So I can't ask for this lollipop.

I handed the lollipop back to her, and handed her the homework book and said, "Osmanthus, you can help me if I don't understand English." So you don't have to give me a lollipop. ”

"Zhou Yu, you misunderstood. I'm not trying to copy my homework. I wanted you to teach me how to solve the last question. Osmanthus explained that it seems that she is a good classmate who hates plagiarism.

I thought about it for a moment, and then replied, "Well, good!

Let's look at the problem first: As shown in the figure, ball A is doing a parabolic motion in the air with an initial velocity of 5 m/s obliquely upward. After 0.3 seconds, ball A reaches its highest point. Then, ball A continues to move parabola, passing through a place with a horizontal distance of 20 m from the starting point of ball A, and collides elastically with ball B, which was originally stationary. And the velocity of ball A after the collision is 10 meters per second. Knowing that the masses A and B are equal, find

The velocity of the ball B after it collides. (g=10m/s², ignoring air resistance calculation, collision energy loss is negligible)

If we see that we are asking about the velocity of the balls after they collide, then we know that the formula can be given by the law of conservation of kinetic energy:

1/2MA*VA²+1/2MB*VB²=1/2MA*VA'²+1/2MB*VB'²

And because the masses are equal and the velocity of the ball B is 0 at rest, the formula can be simplified to:

VA²=VA'²+VB'²

And here we can see that the VA 'knows and wants to ask for VB'.

Then we need to find VA by the formula of parabolic motion.

We see that the initial velocity of ball A is known, and the velocity vector characteristics can be divided into vertical and horizontal velocities. And the vertical velocity we can reach the highest point after 0.3 seconds, that is, the moment when the vertical velocity is 0, we know that the initial vertical velocity of ball A is 0.3g. Through the Pythagorean theorem, the initial velocity in the horizontal direction is known. Then, through these, there is also the horizontal displacement distance, which can be used to know the time when the ball A is parabola. Then we can know that the vertical velocity of the ball A at the moment of collision under the acceleration of gravity, as well as the horizontal velocity of the parabolic motion, are constant. We can again use the Pythagorean theorem to find the total velocity at the moment of collision of the ball A. So bring this velocity into VA² = VA'² + VB'². Now that the two data in the equation are known, then the answer can be obtained"

What is a high school quiz question, that is, to try to be as detailed as possible in the solution process to the point that idiots can understand it in order to get a full score, I believe that my explanation has reached the level that idiots can understand.

"Oh, I see. Thank you, Zhou Yu, you are so good at physics. Under my careful explanation, Osmanthus finally understood, and also praised me for being good at physics.

Actually, this question is very simple, and if you add air resistance, the problem will be more interesting. However, the physical education class.

I watched Osmanthus turn back and write the answer according to the train of thought I had taught, but her lollipop didn't take it back.

I hurriedly said to Osmanthus: "Osmanthus, your lollipop." ”

"That's your lollipop!"

……

When class finally ended, I went in a plastic bag with a lot of snacks. Then pass through a high-altitude flyover.

Our teaching building is Teaching Building No. 2, and Xiaoyan's class is in Teaching Building No. 1. There is a high-rise link bridge between the teaching buildings. In addition, Building 1 and Building 2 are connected. So I walked from the link bridge to Xiaoyan's teaching building.

I remember that the arrangement of the first year of high school classroom this year was 1 class followed the teacher's office, then 2 classes, and then 3 classes.

However, as soon as I walked to the classroom office, I heard something like this: "Zhou Yan, you are going too far, how can you read English books in physics class!"

I looked into the office, and it was a teacher sitting at a desk teaching a timid little girl.

Damn, this turned out to be Xiao Yan and Teacher Li Youquan. How can Teacher Li be like this, so fierce to such a young female classmate!

"Teacher Li!" I barged into the teacher's office.

"Zhou Yan, how can you ...... in class like this" Teacher Li's original words to teach Xiaoyan were interrupted by me. Turned to look at me and said in surprise: "Hey, Zhou Yu, why are you here." Oh, you came to visit me with snacks! Ha, I didn't hurt you in vain when I was a freshman in high school!"

Damn, it didn't hurt me in vain, what does it mean that it didn't hurt me in vain, that is, every physics class asks questions by name, and if I can't answer, I'm punished for standing in class?

I remember when I was a freshman in high school, I went to strangle.

I want to be at the beginning-

A year ago, when I was a freshman in high school, I remember that the first period was chemistry. I was quite serious in class, and not long after the class, the teacher asked me questions and answered questions. I answered, and not long after, I was asked to answer the question, and I was asked to answer the question 3 times in one class. I'm also strange, when class ended, the chemistry teacher walked up to my tablemate Li Haofan's table and knocked on his table, and then Li Haofan shouted to the teacher: "Second uncle!"

I:......

Emotionally, the chemistry teacher asked a question to remind Li Haofan not to read history books in chemistry class.

The second class was physics, and as soon as I started class, I reminded Li Haofan: "Haofan, it's time for physics class, the physics teacher is our homeroom teacher, can you stop reading history books." ”

Li Haofan put away the history book and said, "Oh. ”

Thankfully, he was able to listen to me!, and then he pulled out a new textbook...... Belch...... It's a political book!

Li Haofan is such a person, he reads history books in chemistry class. In physics class, I read politics books. In biology class, you can also read geography books.

I often advised him not to do this, and he said, "Physics is boring, chemistry is boring, and biology is weird." These subjects are uncomfortable to learn, and I can't understand them when I look at them, and I want to sleep when I listen to them in class. And the history is so interesting, and the geography is magical. In politics, Chairman Mao's thoughts, theories, and the three representatives are even more exciting. I really want to graduate from university right away and immediately devote myself to socialist construction!"

After Li Haofan said this, I thought for a long time whether I was wrong or he was wrong. Later, after my dreams in politics, history, and geography were photographed by the teacher in the 7749th class, I finally had an epiphany. It turns out that I'm not wrong, and Li Haofan is not wrong, these personal interests are different. I will sleep in liberal arts classes, and Li Haofan estimates that reading science textbooks will be the same. That's why I hate liberal arts, Li Haofan is irritable with science, and Yu Wenbo only likes sports.

Li Haofan did not listen to persuasion, and the result was that the chemistry teacher and the biology teacher complained to the head teacher. And the physics teacher, who is the son of the homeroom teacher, doesn't know how to teach.

In the end, Li Haofan still didn't change, so the situation became that when I was in biochemistry class, I had to answer the teacher's questions from as little as three and as many as nine questions. And Li Haofan was looking at the geography and history books. But physics class is okay, every time Li Haofan is asked a question in physics class, he must be punished, and then I am asked no less than ten questions. And from time to time I go up to the blackboard to write answers to quiz questions.

That's how my science grades have gone up. And Li Haofan doesn't know why he can still pass without listening to class. And I didn't take lectures on politics, history, or geography, and I only scored more than 30 points in the exam. Therefore, when Li Haofan was in the second year of high school, he went to the top class of liberal arts, and I was in the physical education class. Because that class was counted as 9 subjects.

……

The past is unbearable. And Mr. Li also said that he didn't hurt me in vain, which made me speechless.

"Brother!"

At this moment, Xiao Yan looked at me, and then shouted at me.