A few high school physics questions, high school physics questions?

Here it must be aggravated, because in seconds, gravity is also doing work, (the default situation here is that gravity does not do work, because the displacement in the vertical direction is zero, in this case the instantaneous velocity becomes zero, but if it is known that there is an action time, it is considered that there is a slight displacement and deformation of the land or iron ball).

Question 2: If it is not a nail in the floor that is smashed, but a vertical wall, will it not be added? What about the ceiling?

Generally, I don't take this test, because it's not difficult, and it's purely a momentum calculation.

Same-sex repulsion opposite-sex attraction This is the key idea for solving the problem.

Two copper balls with a certain charge are relatively close to each other, so it is necessary to consider the influence of the charge distribution on the spherical surface on the electrostatic force, the same charge repels each other, the charge moves to the distal end, the actual charge center of gravity is far from the center distance of the sphere, the dissimilar charge attracts each other, the charge moves to the proximal end, and the actual charge center is less than the center distance of the sphere, so there are two conductors with a certain amount of charge f1 are relatively close to each other.

This kind of question is all about considering points and movements, and can be generalized, but there will be no big questions.

The first one: this is a problem of the momentum theorem, which should contain gravitational impulse, because the momentum theorem refers to the impulse of the combined external force = the change in momentum, and you can see the definition to take the direction in the positive direction, (65*10-f)*

The second: the principle is the same as the first, the downward direction is positive, (

Third: f1 "f2 because they are spheres, not point charges, charge distribution problems, the same kind of charge when the charge is distributed distally, their distance is used as Coulomb's law when the center distance of the sphere cannot be used, but when it is greater than the center distance of the sphere, and vice versa, it is less than.

The front wheel of the bicycle isDriven wheelsThe forward force in the horizontal equilibrium (if the bicycle moves in a straight line at a constant speed) is provided by the stem, while the backward force is provided by the friction of the ground against it.

Since they are not at the same point of application, the ground friction has a force effect on the front wheels: rotation, which is represented in the diagram as clockwise rotation.

Therefore,In this case, friction is the cause of its rotation.

[This needs to be different from the situation of the driving wheel, that is, the rear wheel!] This is called "beneficial friction".

The rear wheel of the bicycle is the driving wheel, that is, the transmission force (also called traction) is acting on the rear wheel, and the friction force on the rear wheel is the driving force of the rear wheel.

And the front wheel is driven by the wheel, that is, the rear wheel pushes the front wheel to go forward, and the front wheel receives a forward thrust from the rear wheel, therefore, the direction of friction must be to hinder the forward movement of the front wheel, that is, the direction of friction is opposite to the forward direction, and the direction of friction is backward.

The stress of the two sliders before and after the withdrawal of tension is analyzed, and the change of the staring degree of the acceleration chain of the two sliders after the withdrawal of tension is analyzed according to Newton's second law, and the maximum acceleration value is determined. According to the relative displacement of the two sliders, the displacement size is judged to be shaped; Analyze the velocity relationship at the same moment according to the movement of the slider. The specific process is shown in the figure:

It mainly examines the application of Newton's second law, and pays attention to two points when solving the problem: use the integral method to deal with the conjoined problem with the isolation method, and the spring will not change instantaneously.

A: Before the tensile force is removed, for the whole, according to the equilibrium condition f=2 mg, for q, t= mg, after the tensile force is removed, p is subjected to the left elastic force and friction force and the elastic force becomes smaller and smaller before returning to the original length, and the acceleration of p at the moment of removal f is the largest, so a is correct.

B: After removing the tension, q receives the elastic force to the right and the friction force to the left, and the elastic force is getting smaller and smaller before restoring the original length, so the elastic force is the smallest, that is, when the elastic force is 0, q has the maximum acceleration g, so B is wrong.

cd: From the above analysis, it can be seen that after removing f, the acceleration of early accompaniment p is to the left and gradually decreases from 2 g to g, and the acceleration of q is to the left and gradually increases from 0 to g, and the initial velocity is the same, then the velocity of p is not greater than the velocity of q at the same time, then the displacement of p must be less than the displacement of q, so c is wrong, the answer is: ad

The force is different, the right side is full resistance, and the left side is one resistance and one pull.

Answer: Because the radius of the ball is slightly smaller than the radius of the pipe, only one side of the pipe wall has a force on the ball, and when the movement below AB, the centripetal force is biased towards the upward direction, so it can only be the outer pipe wall.

It has a force on the ball.