Questions about course of Energy conservation

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Homework Help Overview

The discussion revolves around concepts of energy conservation, specifically focusing on the work done by forces in various scenarios involving a rubber band and a bag of groceries. Participants are exploring the implications of force and displacement in the context of work calculations.

Discussion Character

  • Exploratory, Conceptual clarification, Assumption checking

Approaches and Questions Raised

  • Participants are questioning the interpretation of the work done by elastic forces along a trajectory and the conditions under which work is calculated when holding a bag of groceries. There is a focus on the definitions of work and the significance of the direction of forces relative to motion.

Discussion Status

The discussion is active, with participants providing feedback on each other's reasoning. Some guidance has been offered regarding the interpretation of work in different scenarios, and there is an ongoing examination of the assumptions made in the original questions.

Contextual Notes

There appears to be confusion regarding the conditions under which work is calculated, particularly in relation to holding objects stationary versus moving them. Participants are also reflecting on the implications of their answers in the context of physical principles.

physicos
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Thank you for helping me
1-
One end of a rubber band is tied down and you pull on the other end to trace a complicated closed trajectory.If you were to measyre the elastic force F at every point and took its scalar product with the local displacement F*r,and then summed all f these . What would you get ?

I said it would give the overall force of F over the whole trajectory on the rubber band : IS IT CORRECT ?

2- How much work do you do when you hold a bag of groceries while standing still (I said : W= m*g*h) with m mass of groceries and h height of the bag from ground.
How much work do you do when you hold the same bag along a distance d across the parking lot of the grocery store(I said W= mg*d )
IS IT CORRECT ?
 
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physicos said:
I said it would give the overall force of F over the whole trajectory on the rubber band : IS IT CORRECT ?
What do you mean with "the overall force of F over the whole trajectory"?
No, it is not correct.

2- How much work do you do when you hold a bag of groceries while standing still (I said : W= m*g*h) with m mass of groceries and h height of the bag from ground.
What's so special about the ground here? The problem statement did not say you have to pick it up. You are just holding it.

How much work do you do when you hold the same bag along a distance d across the parking lot of the grocery store(I said W= mg*d )
IS IT CORRECT ?
No. Think about the directions of forces and motion.
 
mfb said:
What do you mean with "the overall force of F over the whole trajectory"?
No, it is not correct.

What's so special about the ground here? The problem statement did not say you have to pick it up. You are just holding it.

No. Think about the directions of forces and motion.

1-I meant with the overall force that F*Δr where just particle of work !
2- I really don't know what is so special ! I've copied the exercise as it is !
 
physicos said:
1-I meant with the overall force that F*Δr where just particle of work !
There is no F*Δr in the problem.
2- I really don't know what is so special ! I've copied the exercise as it is !
Sure, but your answer would imply there is something special about the ground...
How much work does a table need to hold something? If you give a similar answer again, where would the table get such energy from? ;)
 

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