I don t know what s wrong with the physics problem, please master

First of all, let me do it, and I will do it with you.

But if it's really wrong, then I think to change the way of thinking to verify it, yes, at the beginning, the relative velocity of the car and the box is 0, and then the relative velocity is also 0, that is, the relative velocity of the box and the car starts from 0 and then decreases to 0. What is the time of that ascent? I think it's seconds, that is, the time it takes for the car to accelerate, and during this time, the acceleration of the box sliding backwards on the car is meters and seconds, and a distance is calculated as meters.

After the car does not accelerate, the relative speed of the box and the car begins to decrease, from the relative speed to 0, at this time their relative acceleration is, that is, all the friction becomes resistance to make the box "relatively stop", the time is seconds, the distance is meters, then! The distance adds up to meters. It seems that it is undoubtedly rice.

If it's wrong, it's that there is no such thing as uniform linear motion.

I looked right, and I did a great job.

What about the question? Why can't I see the question!

No picture, according to your description, it should be A on B and B on the ground.

A and B do not move, and the friction should be static friction.

1.The frictional force of the ground facing B, taking A and B as a whole, and combining F1 and F2, the friction force is opposite to the same magnitude of the resultant force. The meaning of the title f1 and f2 is the same, the resultant force should be 7 New, the direction is the same as f1, the friction force should be 7 new, and the direction is opposite to f1.

The friction force against A and the tensile force on A are a pair of equilibrium forces, so the magnitude of this friction force is the same as that of A, and the direction is opposite.

There is no limb diagram, if f1 pulls a, f2 pulls b and goes in opposite directions.

1.The friction force is 7N, and the direction of the return is opposite to that of f2.

Contrary to f1.

The direction of gravity and friction is perpendicular to each other, and f is horizontal.

The combined force of gravity and friction provides the downward acceleration of the block. a*m=g-f and the block is moving, f=uf, with the increase of time, f gradually increases, so that f increases, g-f decreases, so the acceleration decreases, the acceleration decreases does not mean that the velocity decreases, it is still an accelerated motion, but it is not as fast as the acceleration.

Until a certain time t, f is very large, f=uf is equal to gravity g, the acceleration is 0, as time increases, f is greater than g, and the block decelerates downward until the velocity is 0, it is stationary, and it is nailed to the wall.

Since the block is not moving at this time, the frictional force is no longer equal to uf, but g

The magnitude of the resultant force experienced by the object is equal to the resultant force of friction and gravity.

At the beginning, due to gravity, the object moves downward, f slowly increases, so the kinetic friction also slowly increases, the direction is upward, and the front is less than gravity, so the object has been accelerating downward, and the acceleration is getting smaller and smaller; When the frictional force is equal to the gravitational force, the acceleration is 0, and the object continues to slide due to inertia; The friction continues to increase, the object decelerates and moves, and the acceleration increases because the pressure keeps increasing; Knowing that the object stops, the frictional force at this point is static friction and the frictional force is equal to mg irrespective of the pressure

At the beginning, f is very small, the block slides, the friction is less than gravity, when the friction increases to greater than gravity, the block slows down, and the speed is zero.

It is estimated that you cut corners when copying the topic, and you can't understand it.

The friction force of gravity g is constant and increases with time, and the friction coefficient is u, then the friction force f=ktu.

From the beginning to ktu=g, the block accelerates, and the acceleration decreases from g to 0

After that, the deceleration motion is done to stop the wooden block, the acceleration is upward, and the acceleration increases from 0 to the maximum.

First of all, it can be tested with a hypothesis. It is assumed that m, m are of equal mass. Then xm=dm 2(m-m) is equal to positive infinity, so it's not true.

In terms of solution, in dealing with xm, whether it is a positive process or an inverse process with a co-velocity at the end velocity, it is the same as v0t, i.e.

It should be x=v0t+1 2at 2, so there is something wrong with that equation.

So my column is:

Finally, the common velocity v, the initial velocity of the ball v0, the displacement of the ball s1, and the displacement of the capacitor s2

For the ball: v=v0-(f m)t... 1

For capacitors: v=(f m)t... 2

From these 1 and 2 formulas, the relationship between v and vo is solved.

Then there is the momentum theorem.

For small balls: 1 2mv square - 1 2mv square = -f (s2 + 1 2d). 3

To the capacitor: 1 2mV square = fs2... 4

Use 3 to represent f, substitute 4, and then solve the formula 1,2 to get the relationship between v and vo into 4, and find that the v sides on both sides are eliminated, leaving only m, m, s2, d these four quantities, I solve it is xm=dm 2(m+m).

PS: In fact, the coupling of equations 1 and 2 is actually the derivation process of the momentum theorem, and the so-called learned momentum theorem is just to omit the derivation, and directly use the relationship between v and m to express it, effectively stripping off the interference of time t.

facos60°=fbcos30°

fasin60°+fbsin30°=fc

i.e.: fa = root number 3 fb

Root number 3 fa + fb = 2fc

FA = root number 3 2 FC

fb=1/2fc

fa:fb:fc = root number 3:1:2

The maximum tensile force that the three ropes can withstand is 150N:100N:200N, and the ratio is: 1:2 If it is gradually increased, the OA rope will reach the limit value of 150 at the earliest

fa≤150

fa:fc = root number 3:2

fc=2fa root number: 3=2*150 root number: 3=100 roots, and the weight of the object that can be suspended by the rope does not exceed 100 pieces of number 3

Use the hypothetical method.

Assuming that the OA pulling force reaches the maximum value of 150N, determine whether the OB pulling force exceeds 100N.

At this time, take OA as one side to make a parallelogram, and ob is:

tan60 foa = 150 times the root number three, greater than 100n.

As a result, the OA is not maximized.

Now let's say the OB reaches a maximum of 100N

Then there is: tan30 fob= 3 parts of the root number 3x100 150N, that is, the OB pull force is 100N, OA pull force is 3 parts of the root number 3x100N, then FOC is sin30x100x2 = 100NA: ......

I don't know if you know ......I can't express myself well .........

From the angle given in the figure, it can be seen that if a heavy object is hung at point C, the OA rope is divided into (root 3 2) mg, and the OB rope is 1 2mg, in order to ensure that each rope is continuous, therefore, if the OA rope reaches the maximum, the OB is 50 3 "100, and the OC is 100 3If the OB reaches the maximum value, the OA is 100 3 > 150, which does not meet the topic. So to sum up, the maximum OC is 100 roots3

100 times the root number 3 n

Draw the force analysis, first calculate the tensile force on the OA OC with 100N on the OB to see if it exceeds the bearing range.

Then calculate the tensile force on OA OC with 150N on OA, and finally compare to find the maximum tensile force.

The meaning of the title is that the direction of the resultant force of gravity and the electric field force is just in the direction of motion, but you don't have a diagram, you don't know whether the particles should do uniform acceleration or uniform deceleration motion, fortunately, there is a third question, at a glance, you know that it is a uniform deceleration motion, assuming that the particle is incident from the lower left corner, moving to the upper right, gravity is downward, the electric field force must be to the left, and the trilateral relationship of the 37-degree triangle is 3:4:5, so mg:

eq＝3：4

Bring in the data to find the electric field strength e=(4 3)*10 4, the third question, the work of gravity plus the electric field force is equal to the reduction of kinetic energy, where the vertical displacement is 12, and the horizontal is 16, so eq*, find v under the root number (

1 The material world is colorful, from the vast universe to the microcosm, all of which reflect the constant movement and development of matter, and the following statement related to matter is correct c

A matter is made up of molecules, and molecules cannot be divided Molecules are made up of atomsb The research object of nanoscience and technology is particles smaller than atoms The scale of the molecule is nano-scale c Molecules are composed of atoms, and all kinds of atoms have similar structures The so-called similarity means that atoms are composed of protons, neutrons and electrons.

d. Different states of matter exhibit different properties, which are determined by the arrangement of molecules, and have nothing to do with molecular forces, which is not clear.

2 The following statement is trueb

aThe sun is the center of the universe A long time ago, it has been proven wrong bSolar activity will have an impact on human production and life.

c The eight planets of the solar system have no moons Jupiter, Saturn, Earth, etc. have moons dThe Sun is the only star in the Milky Way The Sun is the only star in the solar system, and there are countless stars in the Milky Way.

Question 1a Analysis: Molecules are made up of atoms, all Question 1a is false.

b Analysis: A nanometer (symbolized as nm) is a unit of length, equivalent to 4 times the size of an atom. So b is wrong.

d Analysis: The different states of matter exhibit different properties that are determined by the arrangement of molecules and are related to molecular forces, because molecular forces affect the structure of matter, and different structures constitute different substances.

Question 2a Analysis: The Sun is not the center of the universe"Heliocentrism said"Just relatively"Geocentrism says"More progress (the center of the universe is not yet known in **).

c Analysis: Jupiter in the solar system, 13 have been confirmed, followed by Saturn, which has been confirmed to be 10.

d Analysis: The Sun is one of the hundreds of billions of stars in the Milky Way.

Question 1: A molecule can be divided into atoms, which are divided into nuclei and extranuclear electrons, b nano-sized substances are generally larger than atoms, and 1 to 100 nanometers are considered nano-scale. All molecules are made up of atoms, and the atomic structure includes the nucleus and extranuclear electrons.

The magnitude of the molecular force determines the melting and boiling point of this substance.

Question 2: aThe sun is not the center of the universe, not even the center of the Milky Way. bThe peak year of solar activity has a great impact on the earth's shortwave communications, airplanes, and rocket flights.

c The Moon is a satellite of the Earth, and Jupiter has more than 60 moons. Most of the stars shining in the sky at night are stars, and there are very many stars in the Milky Way and even in the universe. These questions are very easy to do as long as the basic knowledge is solid.

1. A is obviously wrong, B is also wrong, and I don't explain it. If you really don't know, look up nanotechnology. Molecule c is made up of atoms, which are made up of nuclei and electrons.

Different atoms only have different electrons outside the nucleus, so there are differences in the electrons outside the nucleus, but the arrangement rules are the same, so the atoms have similar structures. dNot all states of matter are determined by the arrangement of molecules. For example, in metals, there are no molecules.

Secondly, when a substance such as water is in its gaseous state and liquid state, the force between the molecules is also different, and the chaotic water molecules in the gaseous state are because the intermolecular force is too small, so it is wrong.

2. A is obviously wrong, C Earth's satellite is the moon, and if you know anything else, you will be vetoed. d is clearly wrong... So it must be b.

Reason: The sunspot movement has a cycle, and its movement will produce strong electromagnetic interference on the earth, which is enough to affect human life, and there are many others, not to mention.

3. In this case, an initial volume is assumed, such as 5. Then let substance A take the x volume and B take the y volume.

Listing: 5x+y=3*5

x+y=5 gives x=5 3 y=10 3

Then the mass of substance A (5 3) * 5 = 25 3 The mass of substance B (10 3) * 2 = 20 3

The comparison between the two is 5:4 and choose C

4. Steel density 7900kg m3 aluminum density 2700kg m3

Let the volume be v7900-2700)v=104

v=1/50 m^3

Then the aluminum mass is 2700*1 50=54kg and b