Author Topic: Physics Discussion HERE ONLY!  (Read 32821 times)

Offline hmh

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Re: Physics Discussion HERE ONLY!
« Reply #240 on: June 06, 2009, 08:25:39 pm »
Erm, man the windmill question was a little depressing  :'(

Anyway, what I did was.. erm

It's hard to recollect  ::)

I guess there was a question before the one where we had to find the mass, where they asked us to find out the power... shwoing all your calculations
Using the efficiency percentage they gave as 10%, I calculated the Energy as 54,000 Joules.
THEN, the E=Pt P= E divided by T. 54000/1 = 54,000 W (watts)

Then, erm, I was really confused for the next one.
I thought about using the Energy formula itself like KE= 0.5 mv2
but then i thought.. if the velocity is halved, how would the mass increase  :-\ cuz technically if the velocity decreased, then the mass of air passing through the turbines should fall...
... So I just used a ratio and got an answer I can't seem to remember  ???

BUT I think I'm wrong. As they said earlier, probably a heavier mass would mean that speed has decreased  :-[
BUT I DID get the fraction as 1/8... These two answers were really difficult   >:(

most people got 1/8... i guess it the correct answer.. hopefully.. or maybe we all are wrong and examiners have something completely different to amaze us wen freeexampapers get the question paper and mark schemes lol ;D
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Offline MR.BooMBastiC

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Re: Physics Discussion HERE ONLY!
« Reply #241 on: June 06, 2009, 08:40:20 pm »
nice...rep kill..

Offline care

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Re: Physics Discussion HERE ONLY!
« Reply #242 on: June 06, 2009, 09:35:27 pm »
Erm, man the windmill question was a little depressing  :'(

Anyway, what I did was.. erm

It's hard to recollect  ::)

I guess there was a question before the one where we had to find the mass, where they asked us to find out the power... shwoing all your calculations
Using the efficiency percentage they gave as 10%, I calculated the Energy as 54,000 Joules.
THEN, the E=Pt P= E divided by T. 54000/1 = 54,000 W (watts)

Then, erm, I was really confused for the next one.
I thought about using the Energy formula itself like KE= 0.5 mv2
but then i thought.. if the velocity is halved, how would the mass increase  :-\ cuz technically if the velocity decreased, then the mass of air passing through the turbines should fall...
... So I just used a ratio and got an answer I can't seem to remember  ???

BUT I think I'm wrong. As they said earlier, probably a heavier mass would mean that speed has decreased  :-[
BUT I DID get the fraction as 1/8... These two answers were really difficult   >:(

why do you think that those wind mills (i can't remember the real name) are built in places with a lot of wind (with a high speed)? because, the faster the wind is, more air passes through the windmill... so, when the speed of wind is halved, than the mass of air is halved... so 1/8 is the correct answer!
« Last Edit: June 06, 2009, 09:37:10 pm by care »

Offline MR.BooMBastiC

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Re: Physics Discussion HERE ONLY!
« Reply #243 on: June 06, 2009, 09:46:30 pm »
ok ppl its past and i think u should forget it

Offline care

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Re: Physics Discussion HERE ONLY!
« Reply #244 on: June 06, 2009, 09:48:13 pm »
i agree :D

Offline sweetie

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Re: Physics Discussion HERE ONLY!
« Reply #245 on: June 06, 2009, 10:49:07 pm »
just one last que.
in da diode que. was it given dat da diodes work in reverse bias??????//
plzzzzzz reply ;) dats my last que. :P

Offline hmh

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Re: Physics Discussion HERE ONLY!
« Reply #246 on: June 07, 2009, 12:12:32 am »
just one last que.
in da diode que. was it given dat da diodes work in reverse bias??????//
plzzzzzz reply ;) dats my last que. :P

I dont think it said it worked reverse or anything like tht.. it jst mentioned tht it shod go from red to black and its normal diode. They were very very trickly placed in diagrams.. I got D as answer.. many ppl put A and C.. no one did B so i guess B is definately wrong.. or possible we are all wrong and B is correct :P who knows.. lool.
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Offline Bani

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Re: Physics Discussion HERE ONLY!
« Reply #247 on: June 07, 2009, 01:24:28 am »
just one last que.
in da diode que. was it given dat da diodes work in reverse bias??????//
plzzzzzz reply ;) dats my last que. :P

I dont think it said it worked reverse or anything like tht.. it jst mentioned tht it shod go from red to black and its normal diode. They were very very trickly placed in diagrams.. I got D as answer.. many ppl put A and C.. no one did B so i guess B is definately wrong.. or possible we are all wrong and B is correct :P who knows.. lool.

I put B :D......I wonder.... :-\ :-[

Offline hmh

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Re: Physics Discussion HERE ONLY!
« Reply #248 on: June 07, 2009, 01:26:31 am »
just one last que.
in da diode que. was it given dat da diodes work in reverse bias??????//
plzzzzzz reply ;) dats my last que. :P

I dont think it said it worked reverse or anything like tht.. it jst mentioned tht it shod go from red to black and its normal diode. They were very very trickly placed in diagrams.. I got D as answer.. many ppl put A and C.. no one did B so i guess B is definately wrong.. or possible we are all wrong and B is correct :P who knows.. lool.

I put B :D......I wonder.... :-\ :-[

oh lool.. i take my words back then.. B is definately not wrong... but it culd be wrong . :P
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Offline Bani

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Re: Physics Discussion HERE ONLY!
« Reply #249 on: June 07, 2009, 02:14:26 am »
just one last que.
in da diode que. was it given dat da diodes work in reverse bias??????//
plzzzzzz reply ;) dats my last que. :P

I dont think it said it worked reverse or anything like tht.. it jst mentioned tht it shod go from red to black and its normal diode. They were very very trickly placed in diagrams.. I got D as answer.. many ppl put A and C.. no one did B so i guess B is definately wrong.. or possible we are all wrong and B is correct :P who knows.. lool.

I put B :D......I wonder.... :-\ :-[

oh lool.. i take my words back then.. B is definately not wrong... but it culd be wrong . :P
:D ;) ;D

Offline Muho

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Re: Physics Discussion HERE ONLY!
« Reply #250 on: June 07, 2009, 03:43:57 am »
the answer for the Diode is C. 2 diodes facing each other wouldn't make a current flow. C was from black to red, and D was from red to black. A and B would have no current because the whole point of the diode is to make the current flow one way, and if the two are facing each other then where the hell will the current flow? xD they say common sense is not common, i certainly agree. -.-
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Offline Bani

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Re: Physics Discussion HERE ONLY!
« Reply #251 on: June 07, 2009, 04:28:03 am »
the answer for the Diode is C. 2 diodes facing each other wouldn't make a current flow. C was from black to red, and D was from red to black. A and B would have no current because the whole point of the diode is to make the current flow one way, and if the two are facing each other then where the hell will the current flow? xD they say common sense is not common, i certainly agree. -.-

Having a bad Physics teacher will lead students like me to give such answers.-.-
so I guess they also say that good teachers are not common, to which I certainly agree,-.- ;)

Offline 17

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Re: Physics Discussion HERE ONLY!
« Reply #252 on: June 07, 2009, 05:17:22 am »
hey guys


You know, in all year 9, we had the worst teacher ever he started the year WITH ELECTRICITY!! HAHA IMAGINE AND WE WERE LIKE WTH IS HE TALKING ABOUT!! Looool


So this year a real expereienced IGCSE physics teacher starting teaching us, we started from the begging and it took us only 4months to finish the whoooole thing, thats by feb!!, then we did past papers like 6 years and everybody was just amazing at physics :)


I found the exam very simple and straight forward, most of it was general physics, no motors no generators etc, :)


Guy what did u get for the diode?? was it A??

Thanks
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Re: Physics Discussion HERE ONLY!
« Reply #253 on: June 07, 2009, 06:24:01 am »
what is the answer to the metal question? i wrote aluminium - which i think is wrong (although i hope they condone it). its probably steel but do u think theyll pardon aluminium?

Offline karim

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Re: Physics Discussion HERE ONLY!
« Reply #254 on: June 07, 2009, 06:30:13 am »
da pressure will be da same, da guy is applying da same pressure but due to da difference in the areaz it pains him more but da guy is applying da same force. :-\