In the case of work done by tensile force, is mechanical energy conserved? Why?

Not. Mechanical energy includes kinetic energy and potential energy, and potential energy is divided into elastic potential energy and gravitational potential energy. According to the kinetic energy theorem:

w=△ek。When only gravity or elastic force does the work, w= ek is also equivalent to ep1-ep2=ek2-ek1 (ep1 is the initial potential energy, ep2 is the final potential energy, ek2 is the final kinetic energy, and the initial kinetic energy of ek1) can be obtained: ep1+ek1=ep2+ek2, the mechanical energy at the beginning and the end is unchanged, and the mechanical energy is conserved.

When there is a tensile force to do work: w = ek is equivalent to ep1-ep2 + w pull + w other = ek2-ek1, so ep1 + ek1 is not equal to ep2 + ek2, the mechanical energy changes at the beginning and end, and the mechanical energy is not conserved.

The condition for the conservation of mechanical energy is that only gravity or elastic force does work, and mechanical energy may remain unchanged in the case of tensile work, but it is not called conservation. The so-called conservation refers to the fact that only kinetic energy, gravitational potential energy and elastic potential energy are converted into each other (it must be transformed and unchanged to be conserved), and no other energy is involved, such as internal energy.

Conservation The object undergoes elastic deformation when the work is done by the tensile force, and the elastic potential energy belongs to the mechanical energy, so the mechanical energy is conserved.

If the work done by the pulling force is equal to the work done by the resistance force (excluding the forces such as gravity), then the mechanical energy is still conserved, and if it is not equal, it is not conserved.

Not necessarily. If the velocity is constant, the gravitational potential energy, the elastic potential energy is conserved. Case-by-case analysis.

You have to look at the algebraic sum of the work done by forces other than gravity and elasticity to see if it's zero, and if it's zero, it's conserved, otherwise it's not conserved.

If there is only tension, gravity, elasticity to do the work, then it is not conserved.

Only when the work done by gravity has such a relationship mgh1-mgh2 mv2 (squared) 2-mv1 (squared) 2 shifts to get mgh1 + mv1 (squared) 2 mgh2 + mv2 (squared) 2, the left is the original mechanical energy, which is equal to the later mechanical energy on the right. When there is a pull force to do work, the above formula cannot be obtained.

The momentum p is mv and the impulse i is equal to ft. Their relationship is mv1-mv2=ft.

Momentum is like the amount of money in your bank card, and impulse is like how much money you deposit or withdraw every time you go to deposit. Every time you deposit or withdraw money, the amount of money in your bank card will naturally change.

The impulse is a measure of the time-accumulated effect of the force and is a vector. If the force exerted on the object is a constant force f that is constant in magnitude and direction, then the impulse i is the product of f and the time t of action. If the magnitude and direction of f are variable, the impulse i is applied to the vector integral operation.

Impulse deflection is usually used to find the force between objects in a short-lived process (e.g., impact), i.e. to estimate the force of an object from the increase in momentum and the time it acts. This force is also known as impulsive force. The unit of impulse in the International System of Units is kilograms per second (kg·m s).

It is usually denoted by an i (uppercase i).

There are many kinds of potential energy, and the ones that are exposed to in middle school are gravitational potential energy, elastic potential energy, electric potential energy, gravitational potential energy, molecular potential energy, etc.

But not all potential energy is under the category of mechanical energy. For example, the electric potential energy and the molecular potential energy above.

Each kind of potential energy corresponds to a conservative force to do work, and the conservative force is the force that does the work independently of the path, such as gravity, the elastic force of the spring, the electric field force, and the gravitational force. You can prove or verify the conclusion that they do work independently of the path, and some of them may be beyond the scope of secondary school physics, but they can be explained less strictly.

For example, when you say that the electric field force does work, the electric potential energy changes, and the kinetic energy also changes. It is advisable to set the electric field force to do positive work, the electric potential energy decreases, and the kinetic energy increases the corresponding value. However, mechanical energy does not contain electric potential energy, it only includes kinetic energy, gravitational potential energy, elastic potential energy, and gravitational potential energy.

Hence the mechanical energy is not conserved. But in this process, the sum of kinetic energy and electric potential energy is conserved, (of course, in the above case, the sum of mechanical energy and electric potential energy is also conserved) and the electric potential energy is converted into kinetic energy.

In general, the conservative force does work, and the sum of the potential energy and kinetic energy corresponding to it is conserved, and the corresponding potential segment Sun bond energy and kinetic energy are converted into each other (taking into account the positive and negative work).

Yes, according to the law of conservation of mechanical energy: within a system of objects where only gravity or elastic force within the system does work, the kinetic energy and potential energy of the object can be converted into each other, but the mechanical energy remains the same. The sum of the kinetic energy and potential energy of the object is called the mechanical energy of the object, and the potential energy can be gravitational potential energy, elastic potential energy, etc.

The law of conservation of mechanical energy is a fundamental law in dynamics, that is, if there is no external force to do work in any system of pure objects, and only conservative forces (see potential energy) do work in front of the source of the system, the mechanical energy (the sum of kinetic energy and potential energy) of the system remains unchanged.

The work done by the external force is zero, indicating that there is no mechanical work input from the outside world; Only the conservative force does the work, that is, only the kinetic energy and the potential energy are converted, and there is no mechanical energy that is converted into other energy, and the conservation of mechanical energy that meets these two conditions is true for all inertial reference frames.

The simplification of this law is: when a particle (or system of particles) moves in a potential field, the sum of its kinetic energy and potential energy remains unchanged; Or the sum of kinetic energy and potential energy does not change when an object moves in a gravitational field.

Implicit in this statement is negligible changes in the kinetic energy of objects (such as the Earth) that generate the field of force. This can only be true in some special inertial frame of reference, such as the Earth's frame of reference.

The electric field force does the work of mechanical energy that is not conserved.

Conservation of mechanical energy: Gravitational potential energy, elastic potential energy, and kinetic energy are collectively referred to as mechanical energy. Only when gravity (or spring force) does work, the gravitational potential energy (or elastic potential energy) and kinetic energy of the object are converted into each other, but the total mechanical energy remains the same.

Only gravity or elasticity do the work. Or the sum of the work done by the external and non-conservative internal forces of the system is zero.

The electric field force does positive work, and the mechanical energy increases; The electric field force does negative work, and the mechanical energy decreases. So, the electric field force does the work of mechanical energy that is not conserved.

Mechanical energy is not conserved, you can consider that at the same height, when the electric field force does positive work, the kinetic energy increases, and vice versa, then no, while the gravitational potential energy does not change at this time, so the mechanical energy is not conserved.