Question regarding systems in work & energy

In summary, the concept of systems in physics can be confusing, especially when dealing with multiple systems. In order to determine when net work becomes zero, one must consider the principles of conservative forces and conservation of energy. In the example provided by the professor, the net work becomes zero because the path is closed and the force of gravity is a conservative force. However, more information is needed to fully understand the example and the concept of system in this context.
  • #1
Aghle Sorkh
1
0
My professor (for some weird reasons) makes us write "system [body(ies)]" whenever we are asked to solve a physics problem for work and energy. Systems make me completely confused because sometimes if we have two or more systems, then the net work becomes zero. My question is this: How do I know when the net work becomes zero? Please give me examples of writing "system _" when solving a question.

If the above doesn't make sense, here is an example:

Suppose there is a mass on the air with 0 initial velocity. Find the final velocity (assuming force of gravity is the only force acting on it). The way our professor asked us to solve it is by writing "system mass & earth"... in which case the work due to gravity apparently becomes zero (??). Please explain situations where net work becomes zero and where net work is not zero when I include Earth on my system... Sorry for the confusion!
 
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  • #2
Welcome to PF;

An example where net work is zero:
The net work about any closed path in a conservative force field is zero.
Gravity is an example of a conservative force.

However, you profs example is odd since the path is not closed. But then, you have not fully described it.
I think you need to take us through the example more carefully.

What I suspect is happening is "conservation of energy": in a closed system the total change in energy is zero.
Since work is change in energy...
 

1. What is a system in the context of work and energy?

A system in the context of work and energy is a collection of objects or particles that interact with each other and can exchange energy. It can be a physical object, such as a ball, or a group of objects, such as a pendulum. The behavior of the system is determined by the forces acting on it and the energy exchanges within the system.

2. What is the difference between an open and a closed system?

An open system is one that can exchange both matter and energy with its surroundings. This means that the system can gain or lose particles, as well as energy, through interactions with its surroundings. On the other hand, a closed system is one that can only exchange energy with its surroundings, but not matter. This means that the total amount of matter in a closed system remains constant.

3. How is work related to energy in a system?

Work is a measure of the transfer of energy from one object to another. In a system, work can be done by external forces on the system, or by the system itself on its surroundings. This work can change the energy of the system, either by increasing or decreasing it. Work and energy are closely related, as work is the transfer of energy.

4. Can energy be created or destroyed in a system?

According to the law of conservation of energy, energy cannot be created or destroyed in a system. It can only be transferred from one form to another. This means that the total energy of a closed system will remain constant, even if energy is transferred between different objects within the system.

5. How can the efficiency of a system be calculated?

The efficiency of a system is a measure of how much useful work it can produce compared to the total energy input. It can be calculated by dividing the useful work output by the total energy input, and multiplying by 100 to get a percentage. A higher efficiency means that the system is able to convert a larger portion of its energy input into useful work.

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