Which Energy Terms Belong to Each Side of the Equation for Different Systems?

[fball558]

i was reviewing for my exam and this was one of the review questions. They don't give us the answers (dont know why it is pointless studying the wrong stuff) so i was wondering if anyone knew the right answers. each system can have more than one answer and here is the problem word for word

Starting from rest, a woman lifts a barbell with a constant force F through a distance h, at which point she is still lifting, and the barbell has acquired a speed v. Let Ewoman stand for the following energy terms associated with the woman:

Ewoman = Echemical,woman + Kwoman (moving arms etc.) + Ugrav,woman+Earth + Ethermal,woman
The change in the kinetic energy of the barbell is (1/2)mv2 - 0 = (1/2)mv2.
The general statement of the energy principle is Esys = Wext. We'll consider terms on the left side of the equation (the Esys side, changes in the energy inside the system) and terms on the right side (the Wext side, energy inputs from the surroundings).

I. System: Woman + barbell + Earth
For the system consisting of the woman, the barbell, and the Earth, which of the following terms belong on the left side of the energy equation (the Esys side)?

(1/2)mv^2
+mgh
-mgh
Fh
none of these terms (left side is 0)
(1/2)mv2
-Fh
Ewoman





For the system consisting of the woman, the barbell, and the Earth, which of the following terms belong on the right side of the energy equation (the Wext side)?

2-(1/2)mv2
-mgh
none of these terms (right side is 0)
Fh
Ewoman
+mgh
(1/2)mv2
-Fh




II. System: barbell only
For the system consisting of the barbell only, which of the following terms belong on the left side of the energy equation (the Esys side)?

3-(1/2)mv2
-Fh
+mgh
(1/2)mv2
Ewoman
Fh
none of these terms (left side is 0)
-mgh




For the system consisting of the barbell only, which of the following terms belong on the right side of the energy equation (the Wext side)?

4Fh
none of these terms (right side is 0)
+mgh
Ewoman
-Fh
-mgh
(1/2)mv2
-(1/2)mv2




III. System: barbell + Earth
For the system consisting of the barbell and the Earth, which of the following terms belong on the left side of the energy equation (the Esys side)?

5Ewoman
+mgh
-(1/2)mv2
Fh
-Fh
(1/2)mv2
none of these terms (left side is 0)
-mgh




For the system consisting of the barbell and the Earth, which of the following terms belong on the right side of the energy equation (the Wext side)?

6none of these terms (right side is 0)
Fh
(1/2)mv2
+mgh
Ewoman
-Fh
-mgh
-(1/2)mv2

 

[anathema]

it is important to understand the principles of energy and how it applies to different systems. Let's break down the different parts of this problem and see if we can come up with the correct answers.

First, we need to understand the energy terms associated with the woman in this system. These include Echemical,woman (chemical energy), Kwoman (kinetic energy from moving her arms), Ugrav,woman+Earth (gravitational potential energy between the woman and the Earth), and Ethermal,woman (thermal energy from her body).

I. System: Woman + barbell + Earth
On the left side of the energy equation (Esys side), we need to consider the changes in energy within the system. This includes (1/2)mv^2 (kinetic energy of the barbell), +mgh (gravitational potential energy of the barbell), and Ewoman (energy terms associated with the woman). Therefore, the correct answer is (1/2)mv^2, +mgh, and Ewoman.

On the right side of the energy equation (Wext side), we need to consider the energy inputs from the surroundings. This includes Fh (work done by the woman in lifting the barbell). Therefore, the correct answer is Fh.

II. System: barbell only
On the left side of the energy equation (Esys side), we need to consider the changes in energy within the system. This includes (1/2)mv^2 (kinetic energy of the barbell). Therefore, the correct answer is (1/2)mv^2.

On the right side of the energy equation (Wext side), we need to consider the energy inputs from the surroundings. This includes Fh (work done by the woman in lifting the barbell). Therefore, the correct answer is Fh.

III. System: barbell + Earth
On the left side of the energy equation (Esys side), we need to consider the changes in energy within the system. This includes (1/2)mv^2 (kinetic energy of the barbell) and -mgh (gravitational potential energy between the barbell and the Earth). Therefore, the correct answer is (1/2)mv^2 and -mgh.

On the right side of the energy equation (Wext side), we need to consider the energy inputs from the surroundings. This includes Fh (work done by

 

[nlightner]

I would first like to clarify that this question is testing your understanding of the energy principle and its application to different systems. The terms in the equations are not necessarily "right" or "wrong" answers, as they represent different components of energy within the system and from external sources.

To answer the first part of the question, for the system consisting of the woman, the barbell, and the Earth, the following terms belong on the left side of the energy equation (the Esys side): (1/2)mv^2, +mgh, Ewoman. These terms represent the kinetic energy of the system, the gravitational potential energy of the system, and the different energy terms associated with the woman, respectively.

For the right side of the energy equation (the Wext side), the terms are: Fh, Ewoman, +mgh. These terms represent the work done by the external force (F) on the system, the energy terms associated with the woman, and the gravitational potential energy of the system, respectively.

Moving on to the second part of the question, for the system consisting of the barbell only, the following terms belong on the left side of the energy equation (the Esys side): (1/2)mv^2. This represents the kinetic energy of the barbell.

For the right side of the energy equation (the Wext side), the terms are: none of these terms (right side is 0). This is because there are no external forces acting on the barbell in this system, so there is no work done by external forces.

Finally, for the system consisting of the barbell and the Earth, the following terms belong on the left side of the energy equation (the Esys side): none of these terms (left side is 0). This is because the system is at rest and there is no change in energy within the system.

For the right side of the energy equation (the Wext side), the terms are: Fh, -mgh. These terms represent the work done by the external force (F) on the system and the change in gravitational potential energy of the system, respectively.

In conclusion, it is important to understand the different components of energy within a system and how external forces can affect the energy balance. It is not about finding the "right" or "wrong" answers, but rather understanding the principles and concepts behind the equations. I hope this helps