Calculating Work and Energy in a Box on a Floor: A Quick Problem

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Homework Help Overview

The problem involves calculating work and energy related to a box being pushed on a floor with a constant force. The subject area includes concepts of work, energy, and friction in physics.

Discussion Character

  • Exploratory, Assumption checking, Conceptual clarification

Approaches and Questions Raised

  • Participants discuss the calculations of work done by the person and by friction, with some questioning the interpretation of total work done. There are considerations about the conventions used in defining work done by friction and whether heat energy should be factored into the total work.

Discussion Status

There is an ongoing exploration of the correctness of the original poster's calculations. Some participants express uncertainty about the conventions regarding friction and total work, while others affirm the calculations presented. Multiple interpretations of the results are being discussed.

Contextual Notes

Participants note the potential confusion regarding the sign of work done by friction and its implications on the total work calculation. There is also mention of the impact of friction on the system, particularly in terms of heat energy, which adds complexity to the discussion.

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Homework Statement



A person is pushing a box on a floor with a 250 N force. The box is moving at a constant speed over 12.75 m.

(a) What quantity of work does the person do on the box?
(b) What quantity of word does friction do?
(c) What is the total work done?

2. The attempt at a solution

(a) W = F * d * cosx = (250 N)(12.75 m)(cos0) = 3187.5 Joules

(b) W = F * d * cosx = (250 N)(12.75 m)(cos180) = -3187.5 Joules

(c) Total work = Wperson + Wfriction = 3187.5 J + (-3187.5 J) = 0
 
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Do you have a question?
Your working seems correct.(I don't have my calculator at the moment)
 
I was wondering if my process for (c) was correct.
 
ThatDude said:
I was wondering if my process for (c) was correct.
Probably not correct, but now I'm unsure of whether there is a strict convention to adhere to on the topic of friction. Were I to answer this as a test, I would have given the one identical answer to all 3 parts.

I wouldn't like to say zero total work has been done, because I can see that heat has been added to the system as a result of the friction. (So I'm tipping that maybe we say the work done by friction is zero.)

We'd best wait on to see what others say.
 
Last edited:
ThatDude said:

Homework Statement



A person is pushing a box on a floor with a 250 N force. The box is moving at a constant speed over 12.75 m.

(a) What quantity of work does the person do on the box?
(b) What quantity of word does friction do?
(c) What is the total work done?

(b) is a negative number.
(c) = (a) + (b)
 
I can see why work done by friction is considered negative. W=F.s, so when motion is in a direction opposite to that of F then one of the terms will have a negative sign. For the block, though, where movement is in the same direction as F then their product will be positive, and positive work is done. Thanks rude man.
 
That means all the answers in the OP are correct
 
adjacent said:
That means all the answers in the OP are correct

EDIT: sorry, hadn't noticed the OP's answers changed. Or maybe I misread them.

In any case, yes, they are now correct if he did the math correctly.
 
Last edited:
The confusion was mine. OP was correct from the start.
 

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