Two high school physics synthesis and decomposition exercises, solved

Because AB is in equilibrium, there is no difference between SO and stationary on the platform.

Analysis of the force on A by FN, F, MgB by A against B'and f'where fn'=fn,f=f', the net force between F and Fn = mg, that is, the force of A on B is mg f=mgsinθ

Second question: Vertical force balance 2fcos = mg so f=mg (2cos).

The first problem is to consider ab as a whole, because it is in equilibrium, the interaction force between ab is the pressure between ab, i.e.

The frictional force between the two is MGSin

The second question, because the resultant force of two f's is 2fcos = mgSo f=mg (2cos).

Question 1: 1: The interaction force between a and b is a support force and a static friction force.

The support force of b to a n m*g*cos direction is directed to the static friction of ab to a, and fba=m*g*sin is upward along the inclined plane in the direction of b to a.

The force of A on B and the force of B on A are a pair of action and reaction forces, and the method is the same as above.

2. The static friction force of A against B Fab=m*g*sin along the downward slope.

Question 2: 2*f*cos = mg

f=mg/(2cosθ)

1. Scalars and vectors:

1) The division of physical quantities into vectors and scalars reflects the use of classification methods to study the physical problems of Qingjiao.

2) The fundamental difference between vectors and scalars is that they follow different algorithms: scalars are algebraic; Vectors use parallelogram rules or triangle rules.

2. Synthesis and decomposition of force

1) Resultant force and component force: If a force acts on an object, the effect it produces is the same as that produced by several forces acting together on the object, this force is called the resultant force of those forces, and those forces are called the components of this force.

2) Synthesis of co-point forces:

1. Common point force.

If several forces act on the same point of the object, or if their lines of action intersect at the same point, these forces are called common point forces.

2. Synthesis method of force.

Finding the resultant force of several known forces is called the synthesis of forces.

If and in the same straight line.

a.Co-direction: The direction of the resultant force is the same as the direction of , .

b.Reversal: The resultant force, the direction and , the greater of the two forces.

Angles to each other – the parallelogram rule of force.

3. Parallelogram rule:

Note: (1) Both the synthesis and decomposition of forces follow the parallelogram rule.

2) The range of the resultant force of the two forces.

3) The resultant force can be greater than the component force, or it can be less than the component force, or it can be equal to the component force.

4) When the two components are at right angles, use the Pythagorean theorem or trigonometric function.

Notes: 1) The synthesis and decomposition of forces reflect the use of equivalent methods to study physical problems.

2) Synthesis and decomposition is a method introduced for the convenience of studying the problem, when replacing several forces with the resultant force, the resultant force must be decoupled from each component, that is, the component force cannot be considered when considering the resultant force, and the same reason is that only the difference or component force is considered in the decomposition of the force, and the resultant force cannot be considered at the same time.

3) The magnitude range of the resultant force of the two forces at the co-permeability point is:

f1-f2|f-f+f2

4) The maximum value of the resultant force of the three forces at the common point is the sum of the magnitudes of the three forces, and the minimum value may be zero.

5) When decomposing the force, it is necessary to identify the actual effect of the force acting on the object, and decompose it according to the actual effect.

6) The orthogonal decomposition method of force is to decompose all the forces acting on the object into two mutually perpendicular axes, and the decomposition is often to find the resultant force (the resultant force in a certain direction or the total resultant force).For more knowledge, you can pay attention to the senior one physics course of Beijing New Oriental Middle School.

The techniques for the synthesis and decomposition of physical forces in the first year of high school are as follows:

Knowledge combing 1, the synthesis of force uses the effect produced by one force (resultant force) to produce the same effect as the effect produced by the joint action of several forces (component forces), and is an equivalent substitution. The synthesis of forces must follow the identity of the object and the simultaneity of the forces.

1) Resultant force and component force: If the effect produced by a force is the same as that produced by the joint action of several forces, this force is called the resultant force of those forces, and those forces are called the component of this force.

The relationship between the resultant force and the component force is an equivalent substitution relationship, that is, if a force is decomposed into two components, the effect of this force cannot be considered if the action of the two components is considered in the analysis and calculation; Conversely, if the effect of the resultant force is taken into account, the effect of each component cannot be considered repeatedly.

2) Common point force: The object is acted on by several forces at the same time, and if the lines of action of these forces intersect at one point, these forces are called common point forces. As shown in Figure (a), a metal rod is placed in a smooth hemispherical bowl.

The rod is affected by gravity and the support force of two points A and B; When the line of action N1 is in equilibrium under the action of three non-parallel forces coplanar to the line of action, the line of action of these three forces must converge at one point, so the line of action of gravity g must pass the intersection point of N1 and N2 0; Figure (b) shows a smooth ball hanging on a vertical wall, which is subjected to three forces: gravity, wall elasticity and suspension line tension.

1.When the 3 forces are in the same direction, the force is maximum, so it is equal to 19n, and when the force is the smallest, it is the maximum force minus all other forces (note that the minimum is 0n), so the minimum value is 0n

2.There is acceleration during take-off, you can know that the upward force received by the athlete is greater than the gravitational force, and the upward force received by the athlete is the support force of the ground on him equal to the pressure on the ground, so the ACD is false, B is correct.

3.As shown in the figure, the resultant force of f2 and f3 is balanced with f1, their resultant force is a reverse f1, and then f1 is rotated 90 degrees clockwise, which is an isosceles right triangle, and the answer is b

dbb, in fact, this kind of topic is the simplest physics problem, the most important way to synthesize and decompose the force is to establish the coordinates, and then decompose the force to the coordinates, and then superimpose or cancel, I'm already in my third year, I don't know how to ask again, thank you!

For the analysis of the force on the node, pay attention to keep g unchanged, that is, the net force of the rope remains unchanged.

The force is analyzed, and then the force along the BC edge is decomposed. Decompose according to orthogonal and then analyze.

The analysis of the force on the ball is shown in the figure above.

To synthesize t and fn, you can use mathematical triangles.

The second question uses the integral method: for the ball and the inclined plane, it can be seen that the friction force cancels out the horizontal component of t, so the direction is to the left, and the magnitude is tsin

Simple: The force decomposition of the ball, the gravity, the support force perpendicular to the inclined plane, and the tensile force in the direction of the rope, because the ball remains stationary, so the three forces are balanced, and the three forces are decomposed in the two directions of the vertical inclined plane and the inclined plane, and the pulling force can be found according to the mathematical knowledge according to the balance of the forces in the same direction.

The friction force of the ground on the inclined plane is horizontal to the left, and the force analysis of the inclined plane is carried out, and the answer can be obtained by breaking them down to the horizontal and vertical directions by gravity, vertical support force, and the pressure and friction of the ball on it

Student. I've done it before. The country really seems to be a common problem.

Of course, you can't take the coercion, together ah. Together, they are part of the title set and don't mean they do.

First of all, this is the force f of the two components, according to the actual effect of the force along the rod. (Imagine that the force in the actual direction of the free end of the two bars is easy to see).

Then it is possible to directly pass the force of force above the problem, on the wall, so that the upper end ignores the role of the role below the level of the object on the wall the balance of the vertical force of the force, so that the balancing force is zero on the force is zero, but the whole system. The interaction between the part and the part.

Gravity must be there, play Mocha around, and then look at the electromagnetic force, not forgetting the known force.

Among them, gravity is vertically downward, elastic refers to elastic force, elastic force includes the support force of the inclined plane to the ball, the pull force of the rope to the ball, and the electromagnetic force is not.

Therefore, the ball receives a total of three forces and decomposes: in two directions, parallel to the inclined plane and perpendicular to the inclined plane, and the rest is the same as on the first floor.

I hope you understand not only the results, but also the methods of analysis.

Three forces act on point A at the same time, so that point A is stationary, that is, these three forces are equilibrium forces, or the net force at point A is zero.

If you make a parallelogram with Fab and G as adjacent sides, the length of its diagonal is equal to the force foa

In any triangle made up of these three forces, there is such a relation:

foa=g cos ) fab=gtan ) let oa reach the maximum value first. foa=20 3n, cos =g from (1) foa=30 20 3= 3 2 so =30

In this case, the fab does not reach the maximum value, which can be verified by equation (2). So the answer is reasonable.

Therefore, in order to make both ropes continuous, the maximum opening angle between the OA rope and the vertical direction is =30

In fact, it is a question of the balance of common forces.

FOA, FAB and FAC form two triangles respectively, and then solve the triangles, and the values obtained by the solution can be verified separately. Since in both triangles, FOA is hypotenuse, so it is solved using sine and cosine.

Answer: a

Idea: First of all, we need to analyze the force, the direction of the rope tension is along the rope direction, the limit case is that the rope tension is 10n, and then use the balance knowledge to train the balance equation in the vertical direction, you can.

Analysis: It's not good to type, I took a screenshot of the handwriting, I can't see it clearly or don't understand it, you can hi me after the question to reflect: first talk about the breakthrough point of this problem, we must accurately analyze the force, grasp the conditions of equilibrium, and establish the equilibrium equation.

Let's talk about the requirements of the college entrance examination, there should be no questions like this in the college entrance examination, but the multiple-choice questions all involve force analysis, and the requirements are relatively high, the question types generally require accurate force analysis and then use Newton's laws, momentum, energy, basically dynamic analysis, process analysis, and in the investigation of electromagnetic problems also require force analysis, in short, test, train people's thinking ability and analytical ability.

A suggestion for learning: For physics problems, I think that many times we are required to be able to accurately analyze the physical process and reproduce the physical situation, so when studying, we must be strict with ourselves to be able to truly understand the requirements of the question, sort out the physical process, and over time will form the ability.

It's not a good drawing, but you can see it.

F1 and F2 are the tensile force of the rope (obliquely pulled upward), and the parallelogram method can find the resultant force of the two tensile forces F, which should be hung on the frame, so F1 = the gravity mg of the frame, and the maximum tensile force borne by the rope = 10N, so F1 = F2> = 10N

The maximum spacing is required, that is, when f1 and f2 are equal to 10n, the f combination is at least equal to the gravity mg=10n, and the angle is 120.

Isosceles triangle, the top angle is 120, the two waists are, and it is easy to choose a at the bottom

Let the tensile force of the rope be n, in order to make the rope continuous, that is, the maximum value of the net force of the rope should be equal to mg, at this time n=10 N. From the synthesis of the forces in the figure, it can be seen that when the net force f=mg, 1 is maximum, that is, the distance between abs is maximum.

So we can get the equation: 2ncos 1=f=mg, solve cos 1=12, cos 1=60°.

From the knowledge of triangles: ab=2sin60°.

The main breaking point of this problem is the equilibrium condition when the rope is continuous, i.e., the resultant external force is equal to the gravitational force. Finally, the distance is found using a simple knowledge of trigonometric functions. Drawing a figure is easy to understand.

I don't need a score, the knowledge wants to tell you, the main knowledge point of this problem, the first force analysis is between gravity and tension, using the parallelogram law to deal with, the second note that as long as the rope is not broken, no matter where it is divided, its maximum bearing force is not changed, that is, the two sections in the figure can each withstand 10n tension, I believe you can solve the rest by yourself.

Support the upstairs, physics was originally realized by oneself, a simple question, and a computer, and word, don't you think it's an exaggeration? I believe that if you ask this question, you must like physics, and the key is to make yourself understand the principle, not the topic.

I'm going to sleep, I'm too lazy to think about it.

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