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Physics Discussion HERE ONLY!
hmh:
--- Quote from: zmnigcse on June 06, 2009, 08:23:37 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 >:(
--- End quote ---
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
MR.BooMBastiC:
nice...rep kill..
care:
--- Quote from: zmnigcse on June 06, 2009, 08:23:37 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 >:(
--- End quote ---
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!
MR.BooMBastiC:
ok ppl its past and i think u should forget it
care:
i agree :D
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