A physics problem about mass. Ask for help

The first time to weigh) first take 6 steel balls casually, 3:3 into 2 trays. There are 2 phenomena:

The first phenomenon is balance balance.

Explain that the steel balls with pores are in the remaining 3. (The second time) take 2 of the remaining 3 steel balls, 1:1 in the tray, the balance of the balance indicates that the last remaining is waste, unbalanced, which is light which is waste.

The second phenomenon: an imbalance in the balance.

Explain that the steel balls with pores are in the light group. (The second time) take 2 of the 3 steel balls that are light, put them in the tray 1:1, and the balance indicates that the last remaining is waste, unbalanced, which is light which is waste.

The nine balls are divided into three piles of three each. If it is flat, it means that the bad ball is in the third pile, and if it is not flat, it means that the bad ball is in the light pile.

If it is drawn, the bad ball is the third, and if it is not drawn, the bad ball is the light one.

Divide into three groups of three.

For the first time, take two groups and put them on both sides, which side of the light waste beads is on that side, and the same weight is in the rest.

The second time take two from the rest and weigh them on both sides, and you will be able to do it later.

For the first time, put any 3 of them on the left board and 3 on the right board, and if balanced, take out the remaining 3 to the next step; If it is not balanced, take out the light side of the 3 to the next step.

The second time, put any one of the 3 balls in the previous step on the left board and 1 on the right board, if balanced, the remaining one is light; If it is unbalanced, the upturned side is light.

Divide the steel balls into three groups in a group of three, and take two of them to weigh. If the balance is balanced, then the ones with stomata are in the other group; If the scales are tilted to one side, the light one is the one with pores. In a group with pores, take any two scales.

If the balance is balanced, then the remaining thing is a steel ball with pores; If the balance is unbalanced, the light one will have pores.

The angle of incidence is (60), the angle of refraction is (30), and if the incident ray gradually approaches the normal, the angle between the reflected ray and the refracted ray will be (large) (fill in the size and so on) at 90°

The angle of incidence is 60° and the angle of refraction is 30° greater than.

Answer: There are two ways to increase friction: increase the viscosity of the contact surface of two objects; Increase the size of the contact surface between the two objects. Another way to increase the resistance of an object is to pull the object behind it and add a reverse force to the moving object.

Xiao Ming apparently used the latter method and did an experiment. (1) As a result of the experiment, Xiao Ming can conclude that as the number of turns of the rope around the cylinder increases, (the ownership of the winding cannot be increased indefinitely!)

After increasing to a certain number of turns, the force to pull the rope is almost zero. The force of pulling the object through the rope can be reduced, and the "speed" of the reduction is noticeably reduced as the number of turns of the rope around the cylinder increases.

2) The conclusion of this experiment has many applications in daily life, such as using a rope to put people down on the top of the mountain, for the safety of the people coming down the mountain, and for the safety and labor-saving of the people on the top of the mountain, it is usually to use Xiao Ming's experimental principle to put the rope around a tree several times. (Don't go around too much, too much and you can't put people down!) ）

For example, our chain bridges, wire ...... for drying clothesWhen it is necessary to fix one (or both ends) of the rope or wire, it is usually used to wrap the rope or wire around a fixed object. Tie a knot again, and the problem is generally basically solved.

3) Xiao Ming's thinking program is: first, he found an object that is more suitable for the experiment (heavy iron lock, soft cotton rope - the softness of the cotton rope can reflect the tensile force of the rope at one end of the spring scale more effectively than the iron wire. fixed round rods, spring scales).

Then connect the objects according to the requirements of the experiment. Then the most crucial step is to press the diagram.

1. Figure. Second, the figure.

3. In the order of Figure 4, do experiments with different number of turns around the round stick to see the experimental phenomenon and effect. And from it, an inductive analysis is carried out to draw conclusions.

Through this experiment, Xiao Ming not only exercised his hands-on ability, but also saw a series of experimental phenomena, and also understood a physical principle in life, and mastered a physics method that can be widely used in life and work. It's a lot of work.

Increasing the contact surface increases friction.

The car has wide tires for increased grip. Mountain bikes and track bikes have different tire thicknesses for different purposes, one needs to increase friction and the other needs to reduce friction.

Gradual.

Increasing the pressure increases the friction.

For the first time, it took 200 s from the time it was emitted to the time it was received, so the distance between the radar station and the aircraft was the speed of light multiplied by 100 s, ie.

3 10 8 * 100 10 -6 = 30000 meters.

The second time, it took 186 s from the time it was sent to the time it was received, so the distance between the radar station and the aircraft was the speed of light multiplied by 93 s, ie.

3 10 8 * 93 10 -6 = 27900 meters.

Therefore, the aircraft flew 30000 - 27900 = 2100 meters in 4s, and the speed of the aircraft was 2100 4 = 525 meters in 4 seconds. Already a supersonic fighter.

Set the velocity v

Since the velocity of electromagnetic waves is very fast relative to the speed of an aircraft, it can be assumed that the position of the aircraft does not change when the electromagnetic waves are emitted and received, i.e.

4v＝（ /

then v 525 m s

My high school and university are the so-called famous brands in the country, and I am also a physics major now, and I have also won the National Olympiad in high school, I am very happy to ask you a question, first of all, you must understand that the process and result of solving a problem is not the most important, the method is king, there will be no original questions in the college entrance examination, and it is considered very lucky to meet similar questions that have been done before, the key is the method, from the problem to see that your foundation is not very solid, then I will tell you a little more detailed, I am always telling my students when I am a tutor, Be sure to understand the meaning of each word in the question, rough means friction, slow represents every point in time You can think that he is a stable state, recognize these two points is the premise of your future analysis, I believe you have learned the solution method of object motion on an inclined plane, then this problem can be regarded as the motion of an inclined plane (circular tangent) with an inclined angle slowly decreasing from 90 degrees to 0 degrees, because each point is an equilibrium state, list the force equilibrium equation to find the relationship between the supporting force t, friction f and inclination angle a: t=mgcosa, f = mgsina, it is obvious that when a changes from 90 degrees to 0 degrees, cosa is increasing and sina is decreasing, so t is increasing and f is decreasing. Write so many words, in order to let you understand the idea of this question, I think what you want to know is definitely not just the answer, but the idea of similar questions, I still have more of my own understanding of studying physics, if you have any questions, you can always find me Email friends, I know the importance of the college entrance examination to a student, so I am happy to help the younger students who are struggling for the college entrance examination, I hope you study well.

Because it is a slow motion, the net force can be considered to be 0.

The insect is subjected to gravity, support force, static friction.

Decomposing gravity along the radius and tangent directions, it is known that the support force increases and the friction decreases.

Options B, C pairs.

Support force f = mgcosx

x is the angle between the circle and the horizontal.

During the climbing process, cosx increases, f increases, and b is selected

There is no relative sliding to indicate that the friction force is always equal to the sliding force (gravity one component), the sliding force f1 = sinxmg, the sinxmg decreases in the climbing process, so the friction force decreases, and CBC is selected

bc.According to the drawing, draw the friction force, the support force, and the gravity force respectively, in which the magnitude and direction of gravity are unchanged, and the friction force is perpendicular to the support force! According to the triangle method, you can draw a picture (mobile phone can't draw), you can draw two eligible pictures, and you can know that the answer is BC

C is definitely C··· Because it does not slip on the arc, the supporting force is equal to the gravitational force! So AB can't be chosen. You can only choose it from the CD...

Choose C,,, the bug is on the spherical surface, the spherical surface has been supporting the bug, so the support force remains the same, and the friction becomes smaller due to the constant gravity and the change of angle in the process of climbing up.

The support force becomes larger, and the friction force becomes smaller.

The support force of the b,c arc towards it becomes larger, and the friction force on it becomes smaller.

When moving upward, the support force increases because the component of gravity that is vertical downward increases. The support force becomes larger, resulting in the force in the tangential direction of the inclined plane becoming smaller, because the resultant force remains the same, so the F friction decreases, AD excludes, choose BC I hope it can help you!

This is a dynamic equilibrium problem, and BC is selected by making a force analysis diagram

I chose A in my answer, but I think the answer is wrong, and the Internet says it's BC

Select C, use similar triangles to solve, the gravity magnitude and direction are unchanged, the support force is unchanged (equivalent to the radius), and the friction force becomes smaller.

Induce electromotive force.

e=k·abcosθ)

t=1(s)

e=iri=kabcosθ/r

bia=mg

b=mgr/ka^2bcosθ

After the fake stove swims for n seconds, the stick leaves the hook and hides the pin.

then there is b=b0+nk

n=[(mgr ka 2bcos)-b0] k, after which the stick will repeatedly bounce up and down on the hook.

This bucket banquet picture is your own thought or the question is given.,If it's the question given.,I feel like this question is wrong.,If you want to empty the silver.,It's a metal finch stupid frame rotates 90°.,You try to do it again.。。。

m= *v = kg m The mass of these samples on the Moon is kg. Cut it in half, then the mass of the remaining part is kg and the density is kg m.