Senior 1 Physics... About the conservation of mechanical energy...

Only gravity does the work, the mechanical energy is conserved, if the mass per unit length of the chain is m'Select the horizontal plane 0 potential energy surface where the desktop is located, and the initial state mechanical energy is.

e1 = -m'ag*a2 = -(ma l)g*a2 final state mechanical energy is.

E2 = -mg(L2 + mV22 by the law of conservation of mechanical energy.

MA L)G*A2= -Mgl2 + MV2 2mgL2 - MGa2 = MLV 2V = root number G(L2 - A2) L

No matter how you look at it, it doesn't look like physics in the first year of high school.

You're so fast.

I don't know how to do this question, so I had to find one, which looks the same, so QQ is it.

When leaving, the equivalent center (and center of gravity) has moved down from the table by 1 2

That is, this part of the gravitational potential energy is converted into kinetic energy.

So you should understand.

The gravitational potential energy is converted into kinetic energy, and the potential energy of the horizontal plane is zero, then the formula is listed as the state 1 on the table: mgh1 + 0 (the kinetic energy at rest is 0) and the state after landing 2: 0 (the ground potential energy is 0) + 1 2mv2 The two are equal to the approximate mass.

Take the desktop as the zero potential surface. Let the mass per unit length of the chain be m

The mechanical energy of the chain when it is released from a standstill.

E1=ma(-A 2)G=-A 2*MG 2 where Ma is the mass of the part of the chain hanging outside the table, and (-A 2) is the height of the center of mass of this part of the chain.

The mechanical energy of the chain when it all leaves the table is.

E2 = (1 2) LMV2 + LM(-L 2) g Conservation of mechanical energy.

A 2*mg2=(lmv2) 2-l 2*mg2 is the velocity of .

v=[g(l^2-a^2)/l]^1/2

Just after the chain leaves the table, the center of gravity shifts down by 1 2 (L-A).

This physical process, when the chain is not off the table, does a free-fall motion with variable acceleration. In the whole process, only gravity does the work, so only the energy function theorem is used to calculate. Therefore, mg*1 2(l-a) = 1 2mv , v can be calculated

It is recommended that you carefully analyze the practice questions in the tutorial book, so as to improve.

1. Let's look at the definition first (what is the conservation of mechanical energy and what is the conservation of energy), and the most important thing to see the definition is to understand the conditions for using these two conservation theorems.

2. Formula reasoning, physical formulas are not memorized, they are derived, you can try it, ask your classmates and teachers if you don't understand, so that you can really understand the first and applicable scope of the formula.

3. Do the problem practice, when you do the two-step work of money, you go to do the problem, do the problem to understand the physical situation first, and then carry out force analysis, see the movement clearly, see the applicable physical definition and formula, combined with the conditions, list the formula (it is best to start from the formula sought, what physical quantities are needed, go to the question to find it, if you can't find it, look at other formulas with this physical quantity), the problem should be solved.

In fact, science is learned in this way, the so-called ever-changing is inseparable, you have mastered the basic formula, everything else can be deduced, this is the initial process of learning science, do more exercises, many things begin to become simple.

The Mathematics Q&A team will answer for you, I hope it will be helpful to you.

Mechanical energy includes kinetic energy and potential energy, and only when kinetic energy and potential energy are converted into each other, mechanical energy is conserved, that is, the sum of kinetic energy and potential energy is unchanged. At this point, only gravity does the work.

Mechanical energy is not conserved when heat energy (friction) or other forces are generated in the process to do work, or other energy is converted.

It is subjected to other external forces, and they are all doing work, but their algebraic sum is 0, and only gravity does the work, and the mechanical energy is also conserved.

I wish you progress in your studies and go to the next level! (

First, mechanical energy is conserved. Therefore, considering the conversion, that is, kinetic energy and gravitational potential energy (elastic potential energy is generally not used), and figure out the relationship between their transformation, since it is conserved, if one is less, the other must be more. And also.

To consider other problems, that is, whether there is an external force to do work or whether there is friction and loss in the system, we must read the question thoroughly, roughly, grasp the word conservation, this kind of problem should not be very difficult.

Here's an example. If an object overcomes gravity and does 80 J of work during motion, then ( a The gravitational potential energy of the object must increase by 80 J

b The mechanical energy of the object must increase by 80j

c The kinetic energy of the object must be reduced by 80j

d Gravity must have done 80 J of work on the object.

You see. Overcoming gravity to do work is gravity to do negative work, so d is not right, and then consider the problem of external force, that is, whether there is an external force to do work on the object, if it is not clearly stated in the title, it cannot be determined that it must be converted from kinetic energy, so there is only a

I wish you all the best in solving the problem and studying hard.

Since mechanical energy is conserved, then this is your only **, you can constantly change your ** style, and you can answer whatever he asks. You're only a freshman in high school now. Only a small part of the contact, if you want to get a high score, you must get rid of rote memorization of applying formulas or something bad method, otherwise you can never really solve a problem, learning, not that you apply a variety of formulas, but formulas or theorems are to tell you a new ** or cheats, in the face of difficulties you have to use something to dismantle difficulties, is something you have to master.

1. Analyze the force and work.

Only when gravity (or the elastic force of a spring) does work, the gravitational potential energy (or elastic potential energy) and kinetic energy of an object are converted into each other, but the total mechanical energy remains the same.

Note that gravitational potential energy is relative, but for a motion process, δh of the initial and final positions is the algebraic difference and has no relativity.

The formula for the conservation of mechanical energy in the initial and final states of a two-column system.

The amount of increase in kinetic energy of the system is equal to the amount of decrease in potential energy.

There are two scenarios:

1.If the springs are counted as being within the system, then the mechanical energy of the system is conserved.

2.If the spring is counted as outside the system, then the mechanical energy is not conserved.

In addition, for some problems such as sudden tightening of ropes and collisions between objects, mechanical energy is generally not conserved.

First of all, the first formula: ek+ ep=0, that is, the sum of the change of potential energy and the change of kinetic energy is 0, secondly, carefully analyze the force to find out which forces do the work and the displacement in the direction (this is the point!). Finally, it should be reminded that the use of kinetic energy theorem or the conservation of mechanical energy does not need to pay attention to the process, the relative position of the initial and final states, and the physical quantities such as velocity are the key.

In addition, if it is the motion of a single object, there is no need to use the conservation of mechanical energy, and the kinetic energy theorem will be more convenient and concise! Hope it helps.

I'm also a freshman in high school, don't worry about my method! ）

This is the law of solution to all mechanical energy conservation problems, you take a look at the package you will know.

It's gravitational potential energy and kinetic energy, it's not difficult.

The models of this problem are all of the system mechanical energy conservation problem type. I think it's better to tell you how to solve a problem than to tell you the answer.

When Figure A B moves S to the right, AB is considered as a whole, and the decrease in the potential energy of the system = the increase in the kinetic energy of the system, and the column formula is:

3mgs=1 2(4m)v2 Note that here is the square of v, that is, the solution.

The same is true for other questions.

List the equations for conservation of energy:

mlg+2/3 mlg= 1/2（mv²）+1/2[m(2/3 v)²]

Get v = root number (30 13 lg).

The whole system is conserved in energy! Finally, the angular velocity at any position on the light bar is the same! This is the key point of the solution, the lowest linear velocity is v= r, then the upper ball linear velocity is 2 3r=2 3v

It would be nice to list the equations for the conservation of mechanical energy:

2mlg= 1/2（mv²）+1/2[m(2/3 v)²]1/3mig

Simplified: mlg + 2 3 mlg = 1 2(mv) + 1 2[m(2 3 v)].

v= (30 13 lg).

Can it help you? ^_