Physical mechanical energy, what is called mechanical energy in physics

First of all, you must know that mechanical energy includes gravitational potential energy and kinetic energy, as long as these two quantities are always conserved, such as moving at a uniform speed on the surface of water.

If there is a change, it is not conserved, such as a uniform circular motion in a vertical plane.

The first is that the mechanical energy is balanced, because it is at a constant speed, so the kinetic energy remains unchanged, and there is also in the horizontal plane, so the gravitational potential energy is also balanced

Second, the mechanical energy is not balanced because even though the kinetic energy does not change, the gravitational potential energy changes

Both are not conserved, and mechanical energy is balanced when only gravity or elastic force does the work. In the first case, there may be frictional force doing the work, and in the second case, there must be an external force other than gravity (equilibrium gravity) doing the work.

It is not conserved, if the friction force does work, the internal energy increases, and it is not conserved.

It is necessary to judge whether the other forces are working or not.

Because the ping pong ball hits the ground, the speed changes abruptly (that is, the size and direction), there will be energy loss, and the total mechanical energy will be reduced.

Let me explain it to you like this:

Is there no speed at the highest point? Then the kinetic energy is zero, and the work is done to overcome gravity, so the gravitational potential energy increases, and because the energy is conserved, it must be converted into energy, so it can only be converted into frictional internal energy, so it is consumed up and consumed down, so there is only energy at the bottom of the inclined plane

1. Because there is air friction in the process of falling, the mechanical energy of the ball will be reduced, so it cannot bounce to the original height.

2. Throw vertically upwards.

According to the kinetic energy theorem, the sum of the work done by the combined external force is equal to the amount of change in the mechanical energy, because the initial kinetic energy is ek

Work is done to overcome gravity, but gravity does it again to the object in the process of falling.

, the work done by the combined external force is 0, then the kinetic energy at the bottom end is still ek, there is no change, but the direction of the velocity changes.

According to the conservation of energy, when the upper is to overcome the frictional force to do the work, when the down, the same is to overcome the frictional force to do the work, and then the whole process of energy conservation is used, it can be known that the kinetic energy at the bottom is.

The answer is that the negative work done by friction when the object slides up is still negative work when it slides down, and the object eventually returns to its original position, and gravity does not do work, so the kinetic energy of sliding back to the lowest end is 1ek-(.

Kinetic energy and potential energy (gravitational potential energy and elastic potential energy) are collectively referred to as mechanical energy!

For example, if a car moving on the ground has only kinetic energy, and the potential energy is zero (with the ground as the reference plane), then the mechanical energy is equal to the kinetic energy; An airplane flying in the sky, that is, it has kinetic energy and gravitational potential energy, then the mechanical energy is kinetic energy and aggravating force potential energy; The kinetic energy of an object suspended by a spring is zero, there is gravitational potential energy and elastic potential energy, then the mechanical energy is gravitational potential energy plus elastic potential energy.

Mechanical energy includes kinetic energy and potential energy. Kinetic energy is the amount of energy that an object has while moving and is equal to one-half of the mass of the object multiplied by the square of the velocity. Potential energy is gravitational potential energy and elastic potential energy.

Mechanical energy is the sum of kinetic energy and partial potential energy, and here potential energy is divided into gravitational potential energy and elastic potential energy. It is mass and velocity that determine kinetic energy; It is the height and mass that determine the gravitational potential energy; The elastic potential energy is determined by the stiffness coefficient and the deformation. Kinetic energy and potential energy can be converted into each other.

Mechanical energy is simply the sum of kinetic energy and potential energy. Mechanical energy is a physical quantity that represents the state and height of an object.

In a system, only the above-mentioned forces (gravity, elastic force) are used to do work, and the mechanical energy is conserved.

Friction is not a conservative force, so it cannot be conserved by mechanical energy when it is done, and the kinetic energy theorem can be used.

The kinetic energy does not increase without beam breakage.

In the end, it remains the same. Because the velocity increases until finally the gravitational force equals the frictional force.

The gravitational potential energy keeps decreasing.

Because the scum limb has been falling.

The mechanical energy is constantly decreasing.

Because there has always been friction to do negative work.

In the whole process, due to the continuous decline of the athlete, the gravitational potential energy continues to decrease, and because the gravity is always greater than the air resistance, there is always acceleration, the kinetic energy continues to increase and make trouble, and also due to the existence of air resistance, a part of the athlete's mechanical energy is converted into internal energy, and heat exchange occurs with the air, and the athlete's own mechanical energy continues to decrease.

When the gravity and air resistance are balanced, the gravitational potential energy of the athlete's land core cover decreases continuously, the kinetic energy remains unchanged, and the mechanical energy continues to decrease.

Hello! You have to understand the meaning of these energies.

In the process where the drag force is not greater than the gravitational force, the drag force is not as large as the gravitational force, so it has a downward acceleration, so the velocity is always increasing.

Kinetic energy is related to the mass of the object as well as the speed of motion. So the kinetic energy is also increased.

The gravitational potential energy is related to the height of the object, and the higher the object, the greater the gravitational potential energy it has. The object is falling, so the gravitational potential energy is reduced.

Mechanical energy is the energy possessed by an object.

When the gravitational force and the drag force are equal, the object moves at a uniform speed and the kinetic energy remains the same, but the gravitational potential energy decreases, so the mechanical energy also decreases.

This question is AD

According to the conservation of mechanical energy: the potential energy of A decreases in the process of sliding downward, while at the same time B moves upwards and the potential energy increases. In the beginning, A moves in a straight line and B moves horizontally, so the decrease in A's potential energy is greater than the increase in B's potential energy.

The decrease in the potential energy of A - the increase in the potential energy of B = the kinetic energy of A and B.

Since there is no friction and no energy consumption, A and B must be able to return to the initial position when moving backwards.

Since there is no energy expenditure, the energy of the system is not in A, it is in B, and A is of course correct.

Question 3 only: From the previous conditions of the question, it can be seen that in t 0 1 second, A and B are relative to each other, the acceleration of A to the ground is a ab*g, and the acceleration of B to the ground is ab B, the ground is *(ma+mb) g mb 1 m s 2

So at t 1 second, the velocity of a is v1 aa*t and the velocity of b is v2 ab*t 1m s, and they are in the same direction.

Because at t 1 second, the motor power is immediately adjusted to p 5 watts, so at this time the motor pulls b plank with the force of f pull p v2 5 N.

At this time, the friction force of A to B is F1 Ab*Ma*G 1 New, and the friction force of ground to B is F2 B Ground * (MA+MB)g 4 New, which just satisfies Bi Yuluo F1 F2, so at this time, for a period of time, the plank B is moving at a uniform speed, but A still continues to accelerate (because the speed of A is less than the speed of B).

The time taken for a velocity to increase from 1m s is t 0 (v2 v1) aa (1 second, i.e. object a is at t 2 seconds moment the velocity is the same as b velocity.

After a and b have the same velocity, they are regarded as a whole, since the friction force of the ground against b is 4 N, it is less than the pulling force of the motor 5 N, so this whole starts to accelerate again, and the acceleration of the whole is a (f pull f2) ma+mb) (5 4) 2+2) m s 2, this acceleration is less than, so a and b remain relatively stationary!

Since the power of the motor is maintained at 5 watts, and the overall hand circle acceleration is less, so the whole is a variable acceleration movement, and the force it pulls the plank b will gradually decrease from 5 Newtons, so AB is always relatively stationary in the future, and it can be seen that at the moment of t seconds, the speed at which they are dismantled is all.

What does horizontal distance mean?

People pulling pulleys on the ground are depleted in the group n=2

The tensile movement is s=nh=2 (the tensile work is w=fs=1250n

The gravitational potential energy of a heavy object increases ep=gh=mgh=100 10 The kinetic energy when lifted ek=w-ep=4000-1600=2400j

l1= l2=

12)(lhh=

The displacement of eggplant panicle at the end of the rope tremor bend is s=h+l1-l2=3m The kinetic energy theorem is applied to the system: fs-mgh=δer=2150j

Here are the steps to the norm:

The work done by thrust w=fs=500n*6m=3000j. (The length of the inclined plane should be 6m, not 6cm).

For physics problems, we must first figure out the concepts, and then bring them in according to the specific calculation formula and the corresponding physical quantities, and then solve them.

In this problem, the concept of work is mainly examined: the work of a force is equal to the displacement of this force multiplied by the force in a certain direction.

So. The work done by thrust w=fs=500n*6m=3000j.

The useful work done by thrust is the work done to overcome gravity, i.e., equal to the amount of increase in gravitational potential energy.

w useful = gh = 2400n * 1m = 2400j mechanical efficiency of the inclined plane = w useful w total = 2400j 3000j =

It is 6m handles. Work is the distance in the direction of the force multiplied by the force. Then the worker pushes the box to the car at a constant speed along the 6m inclined plane with a force of 500n, and the work done is 500*6=3000 joules.

On the other hand, the most direct way to get a box weighing 2400N to a car with a height of 1m is to lift it with a force of 2400N upward, so the work used is 2400*1=2400 joules, so the efficiency of the inclined plane is 2400 3000=

Let's take a closer look at the concept.

The question goes like this:

One. According to the work = force distance = 6m 500n = 3000j

Two. According to mechanical efficiency = useful work divided by total work = 1m 2400n (object gravity) divided by (6m 500n) = 80% That's all said hehe.

Work is the distance traveled in the direction of the force multiplied by the force; Power is the ratio of work to time, that is, the work done per unit of time; Mechanical efficiency is the ratio of the work done by the machine to the increased mechanical energy of the object, i.e., the increase in gravitational potential energy is greater than the work done by the machine.