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 Posted: Thu, 9th Jul 2009 07:01 Post subject: Physics Final |
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Im so dead. my head is all screwed up and im supposed to know 15 chapters worth of stuff by morning and its 12:50am right now.
"two billiard balls of equal mass move at right angles and meet at the origin of an xy coordinate system. Ball A is moving upward along the y axis at 2.0m/s and Ball B is moving to the right along the x axis with speed 3.7m/s. After collision (assumed elastic), Ball B is moving along the positive y axis. What is the final direction of Ball A and what are their two speeds?"
WTh 
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SycoShaman
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Posts: 24468
Location: Toronto, Canada
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| Posted: Thu, 9th Jul 2009 07:15 Post subject: |
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Relevant equations
mAvA + mBvB = mav'A + mBv'B
1/2mAvA2 + 1/2mBvB2 = 1/2mAv'A2 + 1/2mBv'B2
Google is your friend 
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| Posted: Thu, 9th Jul 2009 07:20 Post subject: |
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so basically
KE + PE = KE + PE?
Ball A's KE and PE should equal Ball B's. Well thatl give me the speeds but I cant figure out which direction Ball A goes with KE or PE.
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| Posted: Thu, 9th Jul 2009 08:29 Post subject: |
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don't tell that is what ppl get taught in american colleges.. wtf? that's stuff we do in 9-11th grade here.
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Parallax_
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Posts: 6422
Location: Norway
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| Posted: Thu, 9th Jul 2009 08:33 Post subject: |
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| EZTOF wrote: | | don't tell that is what ppl get taught in american colleges.. wtf? that's stuff we do in 9-11th grade here. |
Welcome to america?  |
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| Posted: Thu, 9th Jul 2009 08:42 Post subject: |
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Its an introductory physics class. Its my first time taking it. Gotta start somewhere 
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| Posted: Thu, 9th Jul 2009 09:01 Post subject: |
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The motion in 2d stuff I remember now. Im having MAJOR problems with fluids chapter and I cant remember poiseuille's equation no matter what i do.
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| Posted: Thu, 9th Jul 2009 09:44 Post subject: |
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Basic momentum and energy conservation problem. Energy has to be conserved (like you said) and total momentum has to be conserved (like Syco said). Combine that you get two sets of equations and voila! (btw don't forget about vectors!!! velocity is a vector! Draw in a Cartesian coordinate system and things should be clearer)
"Quantum mechanics is actually, contrary to it's reputation, unbeliveably simple, once you take the physics out."
Scott Aaronson | chiv wrote: | | thats true you know. newton didnt discover gravity. the apple told him about it, and then he killed it. the core was never found. |
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| Posted: Thu, 9th Jul 2009 10:55 Post subject: |
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| Posted: Thu, 9th Jul 2009 19:36 Post subject: |
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SHit I failed this exam. Im pretty sure I got nothing right. Got 3 hours of sleep plus no food in over over 15 hours = fail.
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| Posted: Thu, 9th Jul 2009 19:59 Post subject: |
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| SycoShaman wrote: |
mAvA + mBvB = mav'A + mBv'B
1/2mAvA2 + 1/2mBvB2 = 1/2mAv'A2 + 1/2mBv'B2
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that means as much sense to me as a Chinese instruction book on atomics
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| Posted: Thu, 9th Jul 2009 20:10 Post subject: |
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Lol well that looks really messy on a computer screen but on paper it looks more organized.
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| Posted: Thu, 9th Jul 2009 20:13 Post subject: |
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no it's just that I have never gone far in matters of maths or physics, pisses me off but they're just complete bullshit to me.
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| Posted: Thu, 9th Jul 2009 21:34 Post subject: |
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| FireMaster wrote: | | no it's just that I have never gone far in matters of maths or physics, pisses me off but they're just complete bullshit to me. |
You will be damn outright awesome at something else though its the way it works.. |
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SycoShaman
VIP Master Jedi
Posts: 24468
Location: Toronto, Canada
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| Posted: Thu, 9th Jul 2009 22:44 Post subject: |
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| FireMaster wrote: | | SycoShaman wrote: |
mAvA + mBvB = mav'A + mBv'B
1/2mAvA2 + 1/2mBvB2 = 1/2mAv'A2 + 1/2mBv'B2
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that means as much sense to me as a Chinese instruction book on atomics |
same to me dude lol I just googled what he wrote and its a common question apparently.
EDIT
Well, I'm sure if I picked up a book and learnt it, it'd get it. I'm pretty good at math. Always one of my strong suits during school and shit. |
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| Posted: Thu, 9th Jul 2009 22:47 Post subject: |
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This is physics Math is just a tool to express the world around you and rules that govern it in a concise and universal way.
"Quantum mechanics is actually, contrary to it's reputation, unbeliveably simple, once you take the physics out."
Scott Aaronson | chiv wrote: | | thats true you know. newton didnt discover gravity. the apple told him about it, and then he killed it. the core was never found. |
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SycoShaman
VIP Master Jedi
Posts: 24468
Location: Toronto, Canada
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| Posted: Thu, 9th Jul 2009 22:49 Post subject: |
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Jesus christ...same difference man.
My point is, if I had it taught to me, I'm sure I'd get it you know? Geez...sorry for not putting the S on math
u grammar nazi......
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| Posted: Thu, 9th Jul 2009 22:57 Post subject: |
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hihi, I just replied to your sentence that you were good with math I meant nothing bad (when you say to physicist that math and phy are the same you'll get sorta this reaction o.O  )
"Quantum mechanics is actually, contrary to it's reputation, unbeliveably simple, once you take the physics out."
Scott Aaronson | chiv wrote: | | thats true you know. newton didnt discover gravity. the apple told him about it, and then he killed it. the core was never found. |
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| Posted: Thu, 9th Jul 2009 23:05 Post subject: |
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| Posted: Thu, 9th Jul 2009 23:32 Post subject: |
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I just emailed my professor giving him a piece of my mind. The final exam was ridiculous. It was 4 questions and we were given the least possible information to solve the problems. Not only that, but for all of the problems, in order to find a missing variable, we had to know other formulas. And sometimes to find the variables in THAT equation required other equation manipulations. Memorizing 15 chapters worth of equations is just not doable especially since this class was only one month (summer session). And the lack of sleep really didn't help either.
Im pretty certain everybody failed the exam. Everybody sitting around me definitely failed. When the exam ended, everyone's face looked like they were attending a funeral.
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b0se
Banned
Posts: 5901
Location: Rapture
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| Posted: Fri, 10th Jul 2009 01:33 Post subject: |
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I never knew maths and physics and i will definitely and surely not learn maths again in my entire life because i hate this fucking shit
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SycoShaman
VIP Master Jedi
Posts: 24468
Location: Toronto, Canada
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| Posted: Fri, 10th Jul 2009 09:30 Post subject: |
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| dingo_d wrote: | | hihi, I just replied to your sentence that you were good with math I meant nothing bad (when you say to physicist that math and phy are the same you'll get sorta this reaction o.O ) |
I know dude. But do I seem like I talk to alot physics professors? lol Don't know any.
Those guys break balls over stupid shit (seen dictations and debates on tv, some are just plain idiotic).
@moose
Ah yes, there's the cat makes me chuckle everytime |
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| Posted: Fri, 10th Jul 2009 09:55 Post subject: |
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| timechange01 wrote: | I just emailed my professor giving him a piece of my mind. The final exam was ridiculous. It was 4 questions and we were given the least possible information to solve the problems. Not only that, but for all of the problems, in order to find a missing variable, we had to know other formulas. And sometimes to find the variables in THAT equation required other equation manipulations. Memorizing 15 chapters worth of equations is just not doable especially since this class was only one month (summer session). And the lack of sleep really didn't help either.
Im pretty certain everybody failed the exam. Everybody sitting around me definitely failed. When the exam ended, everyone's face looked like they were attending a funeral. |
That's called physics. It forces you to think outside of the box, connect things that seem to have little or nothing in common. I like when somebody poses a problem and I guess (on my experience and reason) the right answer. It gives you quite the ego boost
@syco: I think we have a bit of a misunderstanding. I was talking that physicist in general would react in that way, and that it's not your fault...
"Quantum mechanics is actually, contrary to it's reputation, unbeliveably simple, once you take the physics out."
Scott Aaronson | chiv wrote: | | thats true you know. newton didnt discover gravity. the apple told him about it, and then he killed it. the core was never found. |
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SycoShaman
VIP Master Jedi
Posts: 24468
Location: Toronto, Canada
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| Posted: Fri, 10th Jul 2009 09:58 Post subject: |
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Misunderstanding...now I'm confused outright lol
Ahh, doesn't matter anyway man. I know you were breakin balls I do it all the time. Its fun
edited for missing words this time 
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| Posted: Fri, 10th Jul 2009 09:59 Post subject: |
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Damn! You and Leo are fast on replies
"Quantum mechanics is actually, contrary to it's reputation, unbeliveably simple, once you take the physics out."
Scott Aaronson | chiv wrote: | | thats true you know. newton didnt discover gravity. the apple told him about it, and then he killed it. the core was never found. |
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SycoShaman
VIP Master Jedi
Posts: 24468
Location: Toronto, Canada
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| Posted: Fri, 10th Jul 2009 10:02 Post subject: |
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I'm trying to be. I hate leaving in the mid of a conversation but I want to chillax for half an hour before I get to bed.
Only reason I'm up is cuz my girl doesn't start till 11am and works till 3pm.
So I get plenty of spooning time still
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| Posted: Fri, 10th Jul 2009 10:08 Post subject: |
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what time is in Canada right now? You're, what, - 6/7 h form GMT?
"Quantum mechanics is actually, contrary to it's reputation, unbeliveably simple, once you take the physics out."
Scott Aaronson | chiv wrote: | | thats true you know. newton didnt discover gravity. the apple told him about it, and then he killed it. the core was never found. |
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SycoShaman
VIP Master Jedi
Posts: 24468
Location: Toronto, Canada
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| Posted: Fri, 10th Jul 2009 10:13 Post subject: |
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-5 me thinks.
Its 4:05am EST (Eastern Standard Time). Thats basically Ontario and Quebec and the East Coast of the US
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| Posted: Fri, 10th Jul 2009 10:27 Post subject: |
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Oh... You should get some sleep. It's 10 am here. I have to study and I sooo don't want to!
"Quantum mechanics is actually, contrary to it's reputation, unbeliveably simple, once you take the physics out."
Scott Aaronson | chiv wrote: | | thats true you know. newton didnt discover gravity. the apple told him about it, and then he killed it. the core was never found. |
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| Posted: Wed, 15th Jul 2009 16:42 Post subject: |
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| timechange01 wrote: | so basically
KE + PE = KE + PE?
Ball A's KE and PE should equal Ball B's. Well thatl give me the speeds but I cant figure out which direction Ball A goes with KE or PE. |
Can't you just draw the speed vectors that work on ball A then use tan^-1 opposite/adjacent vector to get the angle? |
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