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How to find work via Force and Time

  • Thread starter JRC03
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Homework Statement
How much work is done in holding a 45 N sack of potatoes while waiting in line at the grocery store for 3 minutes?
Homework Equations
W=F*D, F=W/D, D=W/F
So I can across this question in class and there were a multitude of answers, such as 0 work (J), my answer was 8100J based on the fact it doesnt tell you any distance moved, just that its 45N for 3 minutes, so my logic was 45N per second so 45*3(60)=8100J
 

berkeman

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Welcome to the PF. :smile:

If the sack of potatoes is sitting on a table and not being moved for those 3 minutes, it takes zero energy.

But if you are holding it, your muscles are exterting themselves more than if you were just standing there without the sack. So the "energy required" is your increased metabolism.

This recent thread may help you with this...

 

haruspex

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45N per second
No, it is 45N, not 45N/s. N/s would not be a valid unit for a force.
And why would it be per second? Why not 45N/hour?

How much energy you use in holding something depends very much on how you hold it. As Berkeman notes, there is energy required just to keep muscles tense. But you have been given no information on that, so I think you are meant to treat it the same as if the potatoes were tied around your waist, i.e. no tensing required.
 

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