Are you a physics expert? If so, please ask me a question, because neither will the teacher!

It is mainly caused by shocks.

Scientific research shows that under the same conditions, the crystals of water under different ** are different.

Why isn't your appearance much different from everyone else's? A truth.

I'll keep the information on King Elrond in my collection.

Select D, although aluminum is not a ferromagnetic material, but it is a ring type, the magnetic flux through the aluminum ring increases instantaneously when connected to the power supply, according to the Lenz theorem, the movement of the aluminum ring should reduce the magnetic flux through it, so the aluminum ring jumps; Before the power failure, the aluminum ring should have been set back on the core, the moment of power failure, the magnetic flux through the aluminum ring decreases, according to the Lenz theorem, the movement of the aluminum ring should increase the magnetic flux through it, that is, to the iron core, but the aluminum ring has been set on the core, so it can not move.

b. The aluminum ring does not jump at the moment when the switch is closed, and the aluminum ring does not jump when it is disconnected after the switch is closed.

Select B. Because it is an electromagnet it does not attract Lu, so.

People who are more than ten years old, it is better to do less stupid things like copying homework.

For answer A, the change in velocity v2-v1=at, is the product of acceleration and time, if the change in velocity is large, it can only be the product of time and acceleration is large, that is, the acceleration may be small or large, but this question is the choice may be correct, so the answer A can be selected.

For answer b, the direction of change of velocity is the same as the direction of acceleration, so if the direction of change of velocity is positive, then the direction of acceleration is also positive, and this option is definitely false.

For the C answer, the magnitude of the acceleration is to control the speed of the change, and now the speed is changing faster and faster, there must be an increase in the addulin, so this option must be wrong.

For the D answer, as long as the speed changes, there must be acceleration, so this option is also wrong, the answer is to choose A, but it must be noted that I did not say that the greater the change in velocity, the acceleration must be small, or it may be large, the magnitude of acceleration and the magnitude of the change in velocity have nothing to do with it, and the magnitude of acceleration can only be measured by the speed of change, not how much it changes.

Let the inclination angle of the inclined plane be , and decompose the acceleration a into horizontal and vertical directions, with the vertical direction being asina and the horizontal direction being acosThen the supporting force of the ground facing the inclined plane is (m+m)g-masin, and the direction is vertically upward; The friction force of the ground on the inclined plane is macOS, and the direction is the same as that of the acceleration level.

1.The direction of sliding friction is not necessarily opposite to the direction of motion of the object? Is that right?

Right. For example, if you put a small ball between two planks and twitch one of them, the ball will move. The ball is subjected to two frictional forces, one of which is the driving force for the motion of the ball

2. The existence of static friction does not necessarily need to have an external force? Is that right? [This sentence is unprofessional, is pressure considered an external force?] Without pressure, there would be no friction

3。As shown in the picture, if the picture is not good, you will look at it. It's an inclined conveyor belt on which an object is placed, and I think that although the conveyor belt gives the object an oblique upward friction force, the component of the object's own gravity will balance out this friction, right?

So this object should rise at a uniform velocity. Our teacher said that the friction of the conveyor belt is high, so the object accelerates and eventually becomes at a constant speed, so it can be transported. [From stationary to rising at a constant velocity, there must be an acceleration process].

The first one: it doesn't have to be the other way around, for example, static friction is not, and if you are walking with a bucket, the bucket is running forward, but the friction is downward.

Second: If this answer is placed in junior high school, it should be considered correct. But it's not true.

For example, when two objects come into contact with each other, they need to be quietly rubbed, and maybe no external force is needed when they come into contact, but to make them come into contact, the initial source power is needed. So external forces are still needed.

Third: When the object is placed on the conveyor belt, it will produce instantaneous gravitational potential energy, so the conveyor belt will produce instantaneous acceleration until the gravitational potential energy is canceled, and it will move at a uniform speed. [The landlord didn't say that the question was asked or something, so I don't know if it's right].

To sum up, what your teacher said can be regarded as correct.

1.The direction of the sliding friction force must be opposite to the direction of the relative motion of the object, not the direction of motion.

2.That's right, it is also possible to do work with internal forces. ep: Bullets hit wooden blocks.

3.The condition for constant velocity is that the gravitational force along the inclined plane is equal to the frictional force, which is not guaranteed, so when the frictional force is greater than the gravity component along the inclined plane, the block will accelerate upward along the inclined plane (but downward relative to the inclined plane) until the block moves at the same speed as the conveyor belt, moving at a uniform speed.

1.It depends on whether your object is a mass or a rigid body. In the case of a particle, then the sliding friction must be in the opposite direction of motion. Not necessarily if it's a rigid body.

2.The default initial velocity is 0If the initial velocity is equal to the belt velocity, then you are right.

1.Must be the opposite 23

This is explained by inertia, when the object is first put up, the velocity is zero, the final velocity is the belt velocity, the friction is a balancing force, at the beginning, the relative velocity is maximum, the friction is the maximum static friction, the component of gravity is not enough to offset the friction, so the object is unbalanced, so it accelerates uniformly, and then when it accelerates to the belt velocity, the relative velocity is zero, that is, there is no relative displacement, so it is a constant velocity, because it can't accelerate to a higher than the belt.

1.The first question, your teacher is right, sliding friction looks at relative motion.

Child, think about life, imagine a horizontal conveyor belt to the right to transmit an object, and the stationary object A slips after being put on it, and it moves relative to the left relative to the conveyor belt, but is still driven to the right (I myself admire that I can say the phrase "moving to the right" = =).

2.The second question I don't understand what it means, but you can imagine that if an object B rubs A below it and moves in a straight line at a constant speed to the right without slipping, then A is subjected to the static friction of B to the right, and A is only subjected to static friction in the horizontal direction (of course, A is subjected to gravity and support in the vertical direction), I wonder if you mean that.

3.The component of gravity is determined by gravity, not to balance the friction, that is determined by the degree of your inclined plane and gravity, not how much friction it will become, when the friction is greater than the component, there will be an accelerated motion of the object, and finally become a constant velocity.

Okay, I'm finally done typing, for the sake of my reply to the child in the middle of the night, hand over the points, hehe

1.The direction of sliding friction is not necessarily opposite to the direction of motion of the object, right. When you place a small piece of wood on a conveyor belt, the friction is in the same direction as the movement2, and the static friction does not necessarily need to be acted on.

That's right. Force is not the cause of changing the motion of an object. Objects at rest are also subject to friction (static friction)3

You first have to analyze the force, find out which force is greater in the direction of friction and the level of friction, and this problem is solved.

Third, if the sliding friction force is greater than the gravitational component, it should always be in a uniform acceleration motion.

At the moment of opening and closing, the magnetic flux in the aluminum ring increases instantaneously, and according to Lenz's law, a reverse magnetic field will be generated to jump.

The magnetic flux of the closed type decreases, and the co-directional magnetic field does not jump.

d At the moment of closing the switch, the magnetic field in the coil is enhanced, and the magnetic field of the induced current in the aluminum ring will be repulsed by the magnetic field of the coil, and the aluminum ring jumps.

At the moment when the switch is closed and then disconnected, the magnetic field in the coil weakens, and the magnetic field of the induced current in the aluminum ring will attract the same direction as the magnetic field of the coil, and the aluminum ring will not jump.