Those doubts in the second year of junior high school physics, the second year of junior high school

Respect is a virtue. Dale Carnegie, the American master of relations, once said, "Show respect for other people's opinions, don't say anything."

You're wrong'. Schopenhauer once said, "Respect every man, no matter how humble and ridiculous he may be."

One year, a well-known foreign company was recruiting employees for the profession of chief representative of China. In the fierce competition among thousands of people, five students stood out, but only one could be chosen. Among them are two PhDs, two graduate students and one undergraduate student.

When they thought it was an undergraduate, it turned out to be a dumbfounded, and it was only the undergraduates who were selected. The examiner's reason is simple: when the five submitted the materials, only the undergraduate students handed them to the examiner with both hands. Finally, the examiner said:

Respect for others is the most basic requirement. A few years ago, an international choir competition was held in Sydney, Australia, where a children's choir from China competed with more than 100 choirs from all over the world. When the children entered the venue with excitement, they found that among the national flags that had been hung in the entire venue, there was no Chinese flag.

The children's expressions suddenly became grim, because they realized that the lack of respect for their country was more important than the lack of respect for themselves. So, when it was the children's turn to play, they lined up as usual, but one child came out and said to the audience in fluent English:

When we came here, we really wanted to dedicate our singing to friends from all over the world and show the demeanor of our Chinese children. However, we found that our Chinese flag was not hoisted here, and we felt that the dignity of our motherland was at stake. So we refuse to perform!

There was a burst of discussion in the audience, and then a round of applause. People applaud the Chinese children for being able to uphold the dignity of the motherland at the expense of their personal interests. The organizers of the contest rushed to apologize to the children, saying that it was a mistake at work.

So, after watching the five-star red flag rise, the children let go of their beautiful and moving singing ......Learn to respect others and take everyone and everything seriously. It's like a ray of sunshine that brings warmth to others.

Hello landlord. I am a freshman in high school.

The first question is to add up the bunch of data and calculate the average for yourself.

Question 2 Landlord, you must always think about this formula: no matter how the speed changes, including walking and stopping in the middle, the average speed is always the total distance divided by the total time. It can't be as simple as adding up the two velocities and then averaging them.

Question 3 We haven't learned the knowledge points of linear motion with uniform variable speed in high school、。。

For example, how long is an object? (In this question, do you average the middle number from these numbers, or do you calculate it yourself?)

One of the data in this problem is wrong, and that is to add up the remaining data and average the length of the object.

2. In the linear motion of variable speed, I don't tell you how long the distance is, but only tell you that for example, the first half is 8m s, and the second half is 12m s, how to find the average speed? It should be obtained by dividing the total time by the total route.

The last one could not be calculated.

1.Do the math yourself.

2.Let the first half of the journey be S, the second half is also S, and the time is S 8 and S 12 respectively.

3. The last question is out of the curriculum, and you have to learn the linear motion of high school uniform speed change. We have learned, and you don't have to master it in the second year of junior high school, so we won't explain it.

I'm from a key middle school... Trust me!!

1 Find the average.

2.Let a distance s be the same because the two journeys are the same, so write the expression directly and calculate it (2s (s 8+s 12))?It seems to be about the same.

3.I don't have time for the last question, I can't do it.

Upstairs seems to be the right solution.

1. Of course, I count myself.

2. This is the first year of high school, is the initial velocity 0?

3 divide 8 by 100.

The amount of water has decreased, and the amount of antifreeze has changed, but the number of portions has increased, which may be better understood by some specific numbers: for example, there were 10 parts of water, 10 parts of antifreeze, and then the antifreeze content was 50 percent, and now the water has been reduced to 5 parts, and the amount of antifreeze is still 10 parts, and the amount remains the same, but the number of parts it has become larger, and it has become 2 or 3, and the boiling point of the mixture is not related to the content of the antifreeze, but to the fraction he gets.

Antifreeze content % 30 40 50 60 70 80 90 corresponds.

The boiling point of the mixture is 103 104 107 111 117 124 141

Visible Answer: "Elevated; Water decreases due to vaporization and the antifreeze content increases. "It's understandable.

I don't know if you can understand my answer, but the most important point is that the boiling point of the mixture is not related to the actual amount of antifreeze, but to the fraction it takes.

If the mixture is reduced, then the water is reduced. The mass of that antifreeze remains the same.

The content here can be understood in two meanings.

First, the quality contained. Then the answer is the same.

Second, the percentage content. The answer is enlargement.

In general, the content refers to the percentage content, which is the percentage of the percentage

Archimedes was the first to propose the principle of leverage in his book On the Equilibrium of Plane Figures.

He first took some of Archimedes' empirical knowledge of the practical application of leverage"A self-evident axiom"Then, starting from these axioms, using geometry through rigorous logical arguments, the lever principle is derived.

The axioms are: (1) hang equal weights at the ends of weightless rods at equal distances from the fulcrum, and they will balance; (2) Hang unequal weights at the two ends of the weightless rod at an equal distance from the fulcrum, and the heavy end will tilt downward; (3) Hang equal weight at the two ends of the weightless rod at an unequal distance from the fulcrum, and the far end will be tilted down; (4) The action of one weight can be replaced by the action of several evenly distributed weights, as long as the position of the center of gravity remains the same. Conversely, several evenly spaced weights can be replaced by one suspended at their center of gravity; The center of gravity of the figure is distributed in a similar way ......It is from these axioms that in"Center of gravity"On the basis of the theory, Archimedes discovered the principle of leverage, namely"When the duo is balanced, their distance from the fulcrum is inversely proportional to their weight.

Archimedes' study of levers is not only theoretical, but also includes a series of inventions based on this principle. It is said that he once used levers and pulleys to launch a mast boat parked on the beach. During the battle to defend Syracuse from the Roman navy, Archimedes used the principle of levers to create catapults at close and close range, using them to shoot various missiles and boulders to attack the enemy, and once held the Romans out of the ancient city of Syracuse for three years.

It is also worth mentioning here that there have long been records about leverage in the history of our country. The Mohists of the Warring States Period once summarized the laws in this regard, and there are two special records of the principle of leverage in the "Book of Ink". These two articles speak comprehensively about the balance of leverage.

There are those with equal arms, and there are those with unequal arms; There are those who change the weight of the ends to deflect it, and there are those who change the length of the arms to deflect it. Such an account is also very valuable in the history of world physics, and Mozi's discovery was about 200 years earlier than Archimedes.

The principle of leverage was proposed by Archimedes, did you teachers misremember?

Archimedes was very proficient in mechanics, and it is not surprising that he proposed the principle of leverage. His famous quote: "Give me a fulcrum, and I can pry the whole earth." ”

Hello, please describe your doubt.

Questions. When the supply voltage is constant, a branch is opened, will this current become smaller?

When the supply voltage is constant, will the total current be reduced if a branch is broken?

Yes, the total current will be smaller because the total resistance will be larger.

Questions. When the power supply voltage remains unchanged, will the total current be reduced if a branch of the parallel circuit is opened? It is a parallel circuit.

Yes, if a branch of a parallel circuit is broken, the total current will be reduced.

If a branch of a parallel circuit is broken, the total resistance of the circuit will be larger, and the current will also be smaller.

Questions. Is it when the supply voltage is constant? Yes.

(1) 20,000 pa (2) 1 ton is equal to 1,000 kilograms, so 3,000 J (3) 3,000 divided by 20,000 is equal to 15 percent

First of all, because the flag is floating in the air and is floating to the left, it means that the direction of the wind is blowing to the left.

Since the wind blows to the left and torch B floats to the right, the torch must not be stationary, if it is stationary, it should be to the left as the wind direction, so torch B must be moving, since the flame of torch B moves to the right, it means that torch B must be moving to the left, and the speed of movement is greater than the wind speed.

Looking at the torch A, the flame of the torch is the same as the national flag, indicating that the torch may be stationary. Further analysis, if the torch moves to the right, the flame also floats to the left. Think about it again, if the torch moves to the left, and the speed is less than the wind speed, the flame can also move to the left.

So: B torch: Moves to the left, and the speed of the movement is greater than the speed of the wind.

A torch: three cases: 1Rest.

2.Move to the right.

3.It moves to the left and the speed is less than the wind speed.

First of all, it is good to judge that it is B, and it must be that the torch (hand) runs (moves) to the left downwind at a speed greater than the wind speed.

A is possible in all three cases.

1: Headwind moves to the right, and the flame moves to the left.

2: Stationary, the flame is still to the left.

3: If the downwind moves to the left, but the speed is less than the wind speed, the flame is to the left because the relative wind speed is still right to left.

In fact, B is the fourth situation where A cannot exist, that is, the torch moves to the left faster than the wind speed, and the relative wind speed is left to right, and the flame is to the right.

There is also a situation in which the torchbearer moves to the left at a speed equal to the wind speed, so since the relative wind speed is zero, that is, stationary, the flame is vertically upward, which is not the case of A and B on the diagram.

Note: On the reference system, the first is the reference system for the influence of the flame state, which should be the torch itself, and the corresponding affected system is air (wind).

2. The frame of reference for motion is the ground, the main body of motion is the torch (hand) and the flowing air (wind), and the relative motion between them is the sum or difference of these two velocities.

The frame of reference can be determined by adjusting the angle of view in different situations, and it is not necessary to have a frame of reference for all issues.

Let's talk about the state of the flames.

The direction of the flame is always (regarded as flowing) the direction of the air, that is, the direction of the wind, of course, the air for the torch, (of course, there are also relatively stationary cases, that is, there is no relative wind), go with the wind at the same speed, there is no wind, the same reason, the flame is not affected by the wind.

Remarks, (1): Fire is the burning air, so its own inertia is basically ignored, and the air and the surrounding air are integrated, which is regarded as the relative flow of air and torch.

2): The flag simply illustrates the relative movement of air (wind) against the ground, which is an environmental condition.

3) Even if it is the same problem, you can also use different reference frames, and determine that the relative velocity of the relative motion is equal to the sum of the velocity vectors of the respective relative reference frames (this question is the sum or difference), but it is usually better to observe, which varies from person to person, there is no special provision, only the recommendation of the theory.

1.A torch is stationary or moves to the right 2The torch moves to the left and moves faster than the wind speed.