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Author Topic: IGCSE PHYSICS  (Read 23790 times)

Offline @d!_†oX!©

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IGCSE PHYSICS
« on: November 06, 2009, 12:54:41 pm »
A bungee jumper of mass 60kg jumps from a bridge tied to an elastic rope which becomes taut after he falls 10m. Consider the jumper when he has fallen another 10m and is traveling at 15m/s.
Work out how much energy is stored in the rope. Take g= 10m/s2 and ignore air resistance.

now i know this is a pretty easy questioon bt i cant get the answer how to do it....the answer is 5250 J....
i did it by subtracting the k.e from the p.e
but why is it so???

guys help plss
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Offline ~~~~shreyapril~~~~

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Re: IGCSE PHYSICS
« Reply #1 on: November 06, 2009, 01:00:56 pm »
the rope will store PE right??
if not it will have strain energy!!

so if PE then it will be mgh = 60*10*10 = 6000!!

but thatss not the ans so!!
starin energy will be MA = 60*10 = 600!!

but this is also not the ans!!
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Offline @d!_†oX!©

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Re: IGCSE PHYSICS
« Reply #2 on: November 06, 2009, 01:01:54 pm »
dude u took the pe wrong cuz it will be 10*20*60
read the ques carefully shrey!!!
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Offline ~~~~shreyapril~~~~

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Re: IGCSE PHYSICS
« Reply #3 on: November 06, 2009, 01:03:35 pm »
Quote from: @d!_†oX!© on November 06, 2009, 01:01:54 pm
dude u took the pe wrong cuz it will be 10*20*60
read the ques carefully shrey!!!
]
due i have my eyes in place!!!
it says - 10 meters !!
how can you take 20????
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Offline @d!_†oX!©

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Re: IGCSE PHYSICS
« Reply #4 on: November 06, 2009, 01:05:08 pm »
Consider the jumper when he has fallen another 10m

can u read this????so 10 + 10 = 20 m


now dont come up with some other excuse to cover up plssss....
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Offline ~~~~shreyapril~~~~

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Re: IGCSE PHYSICS
« Reply #5 on: November 06, 2009, 01:07:09 pm »
not excuse but i forgot abt it :P :P
we need to subtract PE by KE beacuse it is starin energy right??
and at the time i guess it is PE and just becoming KE so it needs to be subratctd!!!

i guess
lets wait and watch until astar arives!!
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Offline ~~~~shreyapril~~~~

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Re: IGCSE PHYSICS
« Reply #6 on: November 06, 2009, 01:18:58 pm »
By the way is this the ans:
60*20*10=12000
0.5*102*60=3000

so 12000-3000 = 9000!!

as you said i have subtracted PE and KE!!
but not the same ans!!
did i do ne mistake!!
i guess i did!!!
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Offline @d!_†oX!©

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Re: IGCSE PHYSICS
« Reply #7 on: November 06, 2009, 01:19:52 pm »
yeah u did...the speed is 15 not 10!!!!!!! >:(
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Offline ~~~~shreyapril~~~~

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Re: IGCSE PHYSICS
« Reply #8 on: November 06, 2009, 01:20:26 pm »
oh yaa!!
og the mistake!!
it must be 0.5*152*60=6750

so it will be 12000-6750=5250..!!

By the way i also have same wuestion why subtarct???
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Offline Ghost Of Highbury

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Re: IGCSE PHYSICS
« Reply #9 on: November 06, 2009, 01:53:43 pm »
when the jumper is in the middle of his action, the PE stored reduces as it gets converted to KE. Therefore, we subtract the KE from the PE.
i guess this is the answer.
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Offline @d!_†oX!©

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Re: IGCSE PHYSICS
« Reply #10 on: November 06, 2009, 02:06:45 pm »
even i had the same thought in mind...
wt i think is that
elastic energy of the rope+kinetic energy=potential energy
thus, elastic energy=potential -kinetic
i just wanted to confirm it....it'd be gr8 if astar cud say smthng on this....

@shrey dude that's what my question is!!!!!do u like start doing a question sans seeing wat's asked???
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Offline ~~~~shreyapril~~~~

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Re: IGCSE PHYSICS
« Reply #11 on: November 06, 2009, 02:09:32 pm »
we are asking same questions!!
i did not see and copy!!
By the way your logic has sense aadi!!
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Offline astarmathsandphysics

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Re: IGCSE PHYSICS
« Reply #12 on: November 06, 2009, 03:35:22 pm »
60*10*20-0.5*60*15^2=5250
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Offline Ghost Of Highbury

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Re: IGCSE PHYSICS
« Reply #13 on: November 06, 2009, 03:39:18 pm »
Quote from: @d!_†oX!© on November 06, 2009, 02:06:45 pm
even i had the same thought in mind...
wt i think is that
elastic energy of the rope+kinetic energy=potential energy
thus, elastic energy=potential -kinetic
i just wanted to confirm it....it'd be gr8 if astar cud say smthng on this....

@shrey dude that's what my question is!!!!!do u like start doing a question sans seeing wat's asked???

y u getting so hyper?
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Offline @d!_†oX!©

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Re: IGCSE PHYSICS
« Reply #14 on: November 07, 2009, 06:01:07 am »
THanks astar!!!
nd aadi when did i get hyper dude???
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