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Author Topic: When to use Force or Average Force in Work Done?  (Read 1325 times)

Offline tnas11

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When to use Force or Average Force in Work Done?
« on: January 11, 2011, 11:06:42 am »
Im re-sitting Edexcel Physics Unit 1 tomorrow!! Code: 6PH01

When do we use Force x Displacement and Average Force x Displacement in Work Done?

Work Done = Force x Displacement   and   Work Done = F. Average x Displacement

Average Force = Initial Force + Final Force / 2

Its question 21) (a) (ii) (the chest expander question), in "New Template Exemplar" pass paper >> http://www.scribd.com/doc/24557363/GCE-Physics-6PH01

after searching, i understood that we use Average Force when the Force is not constant.. is this right?
so in all springs we use average force?
and what other situations do we use average force?


Exam is tomorrow, good luck to all!! :D
« Last Edit: January 11, 2011, 11:10:21 am by tnas11 »
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elemis

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Re: When to use Force or Average Force in Work Done?
« Reply #1 on: January 11, 2011, 11:08:00 am »
Your link is broken.

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elemis

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Re: When to use Force or Average Force in Work Done?
« Reply #2 on: January 11, 2011, 11:12:00 am »
30 J ?
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Offline tnas11

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Re: When to use Force or Average Force in Work Done?
« Reply #3 on: January 11, 2011, 11:16:17 am »
no its 75J
this is how they solved it, i know how to solve it but i dont get why they used F. Average?

Work Done= F. Avg x Displacement
= 60*5/2 x 0.5
= 75 Joules

My question is when to use Average Force and when to use Force?
i think that average is used when the force is not constant as i found on the internet, but i want someone to tell me this is correct
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Offline The Golden Girl =D

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Re: When to use Force or Average Force in Work Done?
« Reply #4 on: January 11, 2011, 11:19:57 am »
to be honest my teacher is ALWAYS telling us that Work done in a Wire *as in Strain Energy* is measured as follows ;

Work done = 0.5*force*extension.


When to use this ,is whenever they ask your for Work Done in a material that has elastic potential energy in it *in this case Spring*.

Hence,

Work done = 0.5 *force * extension * 5    blue ; cuz there are FIVE springs ;)
               = 0.5 *(60) * ( 0.5)  * 5
               = 0.5 * (30) * (5)
               = 0.5 * 150
               = 75 J

good luck to u too ;)
« Last Edit: January 11, 2011, 11:33:14 am by Miss Invisible »
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Offline The Golden Girl =D

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Re: When to use Force or Average Force in Work Done?
« Reply #5 on: January 11, 2011, 11:35:46 am »
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Offline tnas11

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Re: When to use Force or Average Force in Work Done?
« Reply #6 on: January 11, 2011, 11:39:10 am »
oh yeah!!!! like the area under the force-extension graph = work done!

Area under graph = work done = 1/2 x force x extension!!!
thanks that made me connect the ideas together! :D

no but Work Done = Force x Distance!

and as you said
Power = Work Done/Time
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Re: When to use Force or Average Force in Work Done?
« Reply #7 on: January 11, 2011, 11:41:14 am »
I removed the Post Since I noticed it was displacement NOT velocity *my bad *
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Offline tnas11

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Re: When to use Force or Average Force in Work Done?
« Reply #8 on: January 11, 2011, 11:44:54 am »
yeah no problem.. but thats for reminding me to connect both ideas :D
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Re: When to use Force or Average Force in Work Done?
« Reply #9 on: January 11, 2011, 11:45:27 am »
Your Welcome :)
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