Physics short answer questions

Light travels in a straight line in the same homogeneous medium, the air above the burning stove is less dense and unstable, the light is refracted during propagation, and the image formed on the retina is unstable, so the object seen is shaking.

When light travels, it is refracted in different media.

On the other hand, due to the different temperatures, the molecular movement is either fast or slow. So a lot of different densities are formed in a space. It can be seen as a mix of many different very small media.

Because of the movement of the molecules at the same time, the density is constantly changing, and when it is refracted to the eye, it feels like the object on the other side of the furnace is shaking. Study hard! That's what the university talks about.

It's a matter of light distortion.

If we want to see objects, we need light to enter our eyes, and the light rays are basically along a straight line, unless the density is uneven, and when we see things through the stove, it is because of the temperature change that the air flows, so that the air above the stove is unevenly dense, resulting in the torsion of light, and what we see is twisted according to the imaging principle.

This phenomenon is called shaking light because the refractive index of light in different media is different. The stove heats the air above and has an uneven density. The propagation of light is thus affected by the different refractive indices, resulting in what looks like it is shaking.

When the furnace is burning, the hydrogen reacts with the oxygen element to form water vapor, and it rises, and the refractive index of light in the air is different from that of water vapor, and it goes up, so it looks shaky and distorted.

Upstairs, where does the hydrogen come from in the stove?

When the fire moves, it drives the surrounding air to move, resulting in the illusion of human vision, which looks like shaking!

The fire heats the gas, the air density decreases, and at the same time the hot air rises and the cold air descends to form a convection current.

The refractive index (n) of light is different for different densities of air, and when we look at objects behind us through different densities and changing densities, the transmitted light will change the angle and produce a sense of shaking.

Summary. ab There is also very thin air at an altitude of 400km, assuming that no energy is replenished, under the action of air resistance of the space station, the space station has to overcome the resistance to do work, the mechanical energy of the system decreases, the rate decreases, the space station will do centripetal motion, and the angular velocity will become larger, so ab is wrong; cd 。The first cosmic velocity is the maximum orbital velocity and the smallest launch velocity, the second cosmic velocity is the launch velocity that is free from the constraints of the earth, the orbit of the space station is a circular orbit with an altitude of about 400km, and the orbital radius is greater than the radius of the earth, so the actual space station operation speed is less than the first cosmic velocity, and it is also less than the second cosmic velocity, so c is correct and d is false.

Therefore, c.

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ab There is also very thin air at an altitude of 400km, assuming that no energy is replenished, under the action of air resistance of the space station, the space station has to overcome the resistance to do work, the mechanical energy of the system decreases, the rate decreases, the space station will do centripetal motion, and the angular velocity will become larger, so ab is wrong; cd 。The first cosmic velocity is the maximum orbital velocity and the smallest launch velocity, the second cosmic velocity is the launch velocity that is free from the constraints of the earth, the orbit of the space station is a circular orbit with an altitude of about 400km, and the orbital radius is greater than the radius of the earth, so the actual space station operation speed is less than the first cosmic velocity, and it is also less than the second cosmic velocity, so c is correct and d is false. So chosen:

c 。1 (8 points) October 12, 22, China's space knot "Tiangong class third lecture, this is the first day of China's flight experiment to teach, it is known that the height of China's space station above the earth is, the radius of the sphere is r, and the velocity of the earth's surface is g to find (1 The speed of the Chinese space station moving in a uniform circle around the earth; (2) Due to the existence of a uniform dilute gas with a density in the orbit of the space station, in order to maintain the space station to do a uniform circular motion in a fixed orbit for a long time, it is necessary to add a power force to the space station with the same velocity direction, if the area of the space station in the direction of vertical velocity is s, and the gas velocity is immediately the same as the velocity of the space station after it is hard to thin gas, find the magnitude of the space station acceleration force f.

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Pro, 1The Chinese space station takes 90 minutes to orbit the Earth and flies at a speed of kilometers and seconds.

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Dear, China's Tiangong space station, the current speed is kilometers per second. kilometers per second. This means that 15 and a half times a day around the Earth, about one and a half hours.

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16 questions. Thank you, teacher, for writing me the whole process.

The main thing is to judge the force on the rope, and then after Min Min analyzes the force on the two blocks separately, calculates the acceleration and the degree of content, and the laughter can solve this problem <>

In a narrow sense, vibration refers to mechanical vibration, i.e., the reciprocating motion of an object in the vicinity of a certain location. Fluctuations are the propagation of vibrations and at the same time the propagation of energy. The propagation process of mechanical vibration in an elastic medium is called mechanical wave, and the propagation process of electromagnetic vibration in space is called electromagnetic wave.

The teacher will sort out the relevant physics questions for youRelationship Between Vibration and Wave Answer: In a narrow sense, vibration refers to mechanical vibration, that is, the reciprocating motion of an object near a certain position.

Fluctuations are the propagation of vibrations and at the same time the propagation of energy. The propagation process of mechanical vibration in an elastic medium is called mechanical wave, and the propagation process of electromagnetic vibration in space is called electromagnetic wave.

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Dear classmates, the answer to the second ** is proved to you by the teacher in the form of **.

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16 questions about the teacher.

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Dear you only send 15 and 18 questions to the teacher.

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Dear students, the first question is the speed calculation method, and the teacher will send it to you in the form of **.

Summary. 1) Because the magnetic field force does not do work, according to the kinetic energy theorem 1 2mv -1 2mv0 =qelv= (2qel+mv0 ) m) = 2

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Good. 1) Because the magnetic field force is not good, the work is done according to the theorem of moving the head of the shirt 1 2mv -1 2mv0 =qelv= (2qel+mv0 ) m) m) = 2

Due to the high difficulty of the questions, we can only help you answer the first 2 questions.

The ship is marked with a line, so the displacement of the two times is equal, then the buoyancy they are subjected to is also equal.

From the force analysis, it can be seen that they are only affected by buoyancy and gravity, and they are all stationary. Then gravity is equal to buoyancy, and then buoyancy is also equal, so it can be measured that their weight is equal.

Let's take a standard of elementary school or junior high school or high school. It's hard to say that this is complicated.

Simple idea: f float = g row object float f float 1 = g elephant f float 2 = g stone The ship sinks to the same place g row is the same f float 1f float 2 is the same then g elephant = g stone I don't know the format of the area, I don't understand what I'm talking about.

The pulleys seem to be too small, guess it should be.

1.Uniform deceleration movement.

There are several points in this question.

a.Conveyor belt friction.

b.The dynamic friction is constant.

When the object and the conveyor belt are displaced, the frictional force acts at a distance of l, and the object at point B is thrown at a velocity vb. At w=4, vb is the same as w=0, so the frictional distance is still l. But then as W increases, so does VB.

It shows that the friction force action distance decreases, and the friction force will disappear only when the object velocity is equal to the conveyor belt velocity, so when w=4, the conveyor belt velocity wr is equal to.

d.When w is greater than 4, the earlier the object moves with the conveyor belt as w increases, that is, the friction force action distance decreases. When the wr is greater than or equal to V, the object is subjected to forward friction from the moment it touches the conveyor belt, and accelerates to the same speed as the conveyor belt.

When w>=28, the accelerated motion of the l distance cannot increase the velocity of the object to the velocity of the conveyor belt. The final velocity of the object vb remains at w=28, i.e., vb=wr=28*

Therefore. 2.Let the friction force be f

This gives us v=53Analyze the flat tossing motion at one point w=0.

The muzzle velocity is equal to 4*, the distance traveled.

The height of point b can be derived.

The second one of the drawings does not understand, it is not good.

The first question is that since the object moves flat from B, it takes the same time to land and the same horizontal displacement when W 0<4, that is to say, the horizontal initial velocity of the flat throw in this range is the same, that is, it moves in a straight line at a uniform speed between AB.

The second question is v=w*r=w*

The third question: when w=4, the horizontal displacement is so time t=s v=g, take 10 to get the height h=1 2*g*t 2=