Problems in the physics of life, questions about physics knowledge

No contradiction You misunderstood that molecules that attract each other do not fit close together when the distance between molecules d=r gravitational force = repulsive force; In other words, "the experiment of the lead blocks close together shows that there is a gravitational force between the molecules", and the distance between the molecules must be at least greater than r, how can they be close together?

There is no contradiction, there is a certain relationship between the gaps between molecules and their gravitational pull. It's like pouring sand into a bag full of stones, it's just that their radius is different. Similarly, diffusion is between different molecules.

The gravitational attraction between molecules is different... It is advisable to take a look at the elective content of the chemistry book in high school.

There is no contradiction, there is both gravity and repulsion, and the two maintain a balance.

There is no contradiction, the theorem is right, it doesn't matter what you do, just remember it.

This is not a contradiction at all.

First of all, the force of the molecule is the force of this nature, it is divided into two forces, people who have not studied physics only need to know that they are two different forces, and then these two forces are one of mutual attraction and one is mutually exclusive, the force of mutual attraction acts at a long distance, the distance decreases with a decrease in radius, and the repulsion force is just the opposite (of course, when the distance is more than 10 times the radius of the molecule, both are small).

This is the narration of two forces.

Molecules move at high speed under the action of these two forces, the distance is dominated by gravity, and when the distance is close, the repulsion force is dominant, the closer the distance, the greater the repulsion, which is the reason for the gap (there are deeper reasons), when the distance is far, the gravitational force becomes larger, which is the reason why the matter can be aggregated together without falling apart.

More detailed to read the book, typing is too tiring.

1. To generate current, there must first be an electromotive force, which is determined by the formula of Faraday's law of electromagnetic induction: d = -d dt

That is, the magnitude of the induced electromotive force is equal to the rate of change of the magnetic flux. That is, in order to generate an electromotive force, there must be a change in magnetic flux. In order to generate induced current, there is also a condition that must be met, that is, the line must be closed. Example: A generator generates electricity to make a light bulb glow.

2. The most fundamental formula of induced electromotive force is the above d = -d dt, that is, the induced electromotive force is determined by the rate of change of magnetic flux. Specifically, it can be divided into two types of situations, one is induced electromotive force, and the other is dynamic electromotive force. According to Faraday's theory of electromagnetic induction, a non-electrostatic force is necessary to generate an induced electromotive force.

That is, there is a non-electrostatic field. The non-electrostatic field is generated by a changing magnetic field. The magnitude of the electromotive force is determined by the following formula:

db dt·ds, i.e., the double integral of the magnetic induction intensity to the area of the differential pair of time. From a macroscopic point of view, it is determined by the rate of change of magnetic induction intensity and the rate of change of area. For the kinetic electromotive force, its non-electrostatic field strength is equal to the speed fork multiplication induction strength of the electrons in the rod moving with the rod.

Whereas, the magnitude of the electromotive force is equal to the integral of the length of the non-electrostatic force pair. Qualitative can be understood as determined by the velocity and the length of the rod perpendicular to the direction of the magnetic field.

1.There is a varying magnetic field.

The phenomenon is power generation.

2.Number of turns of the coil, amount of change in magnetic flux, time or magnetic induction intensity, effective length of wire, velocity.

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Analysis] Due to inertia, the horizontal velocity of the bomb leaving the aircraft is the same as the velocity of the aircraft, so when the bomb lands, the aircraft must be directly above point P, A is correct and B is wrong; But when the ** sound reached the pilot's ears, the plane flew some distance westward, so D was correct and C was wrong

Choosing answer A, since the air resistance is not counted, the horizontal velocity of the bomb is the same as the flight speed of the aircraft, so before the bomb does not land, the plane and the bomb are in a vertical line, (so when the bomb lands, the plane is directly above point P), after landing, the horizontal velocity of the bomb is reduced to 0

AD shells are fired with the same horizontal velocity as airplanes, so the horizontal displacement is the same for the same amount of time. While the speed of sound is 340m s, it takes a certain amount of time to propagate to the high altitude, during which time the aircraft flies some distance to the west. Therefore, when the ** sound is heard, the plane is a little west of the ** point.

Because the inertia of the bomb maintains the initial state of motion at a constant speed, and the aircraft reaches the target at the same time, so at this time the aircraft is above, and the sound propagation time is longer, and the aircraft has already flown over the target a little west when it arrives at the plane, so AD is selected

AD (Horizontal speed is unchanged, choose A.)When the sound reaches the plane, the plane has already flown directly above, select d).

Let the masses of A and B guess C are x, y, and z respectively

Rule. 2x = 5y

2x = 4z

4y = 3z + 1

Solve the above-mentioned system of equations for the three-element wide beam shirt.

Available. x = 10

y = 4z = 5

I think I can make equations.

Let A be guessed vertically as x, B as y, and C as Z

Equations can be listed.

2x=5y2x=4z

4y=3z+1

Solution. x=10

y=4z=5

1.By placing the scale perpendicular to the glass plate, it is possible to roughly measure the depth of the container closed by the thin glass plate, which is characterized by the use of plane mirror imaging; When the measurement is observed, the image of the scale is the imaginary (fill in "imaginary" or "real") image of the scale.

2.I choose B by all means. (Socket A is connected in series in front of L2, which affects the work of L2 and will not light up at all).

a, the connection is correct.

C, L2 is also connected incorrectly, but it does not affect other electrical appliances, i.e. L1.

D, Socket B is also wrong and should not be connected in series, even then it will not affect which appliance is used.

Hope it helps, thank you!

1 Void What you see through the glass is the virtual image created by refraction.

2 Except L1 is wrong.

Combined with the force balance and the relationship between mass, density, volume, and weight with mass and acceleration, it can be easily solved.

It's a very simple question, and it all uses the same theorem. I won't give you the calculations, you can calculate them yourself based on my analysis. Hope it helps.

1: In physics, the density of water is used as a known value, while the density of iron cannot be used as a known value, unless it is told in the question. 1 buoyancy is equal to the gravity of the water discharged, how much does 100 cubic centimeters of water weigh (note that it is converted into units)?

2. Balanced force, gravity = spring tension + buoyancy; 3. If the buoyancy is greater than the gravitational force, then it is definitely hollow; If the buoyancy is less than the gravitational force, then it is not certain whether it is hollow or not, but it is possible.

2.Or Archimedes' theorem, buoyancy is equal to the gravitational force of the liquid, as in the first question, the stone and the iron ball are regarded as completely submerged in the liquid, the volume of the liquid is equal to the volume of the object itself, gravity = spring tension + buoyancy, spring tension = indication.

3.This problem is similar to the previous one, except that the known situation has changed, and the same theorem is used, the weight of the ball is known, the pulling force is known, and the buoyancy force can be obtained, then the volume of the water discharged, that is, the volume of the metal ball. The density of the metal ball is known, if it is solid, then the calculated weight should be the same as the weighed, if it is larger than the weighed weight, then it can be judged that it is hollow, and there is no situation that is smaller than the weighed out.

No answer!

1. (1) 1 2at 2=s (2) f=ma to find the resultant force in the horizontal direction, and then the force analysis shows that the traction force is greater than the friction force, that is, the resultant force is the traction force minus the resistance.