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March 29, 2024, 05:15:16 am

Author Topic: VCE Physics Question Thread!  (Read 603321 times)  Share 

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sydneyboy

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Re: VCE Physics Question Thread!
« Reply #135 on: August 25, 2013, 05:48:55 pm »
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v = radius * angular velocity
= rw

v^2/r = (rw)^2/r = w^2*r
Or v^2/r = (2pi*r/t)^2/r = 4pi*r/t^2

The second form is probably more useful, so if you keep the same distance and period you'll be fine. I don't know about the practicalities of that though.

Thanks, so i will select a time to make the period for every test i do and also raidus.. however do you know how i would go about keeping period the same w/o increasing speed (because it increases my r)

lzxnl

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Re: VCE Physics Question Thread!
« Reply #136 on: August 25, 2013, 06:04:17 pm »
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Thanks, so i will select a time to make the period for every test i do and also raidus.. however do you know how i would go about keeping period the same w/o increasing speed (because it increases my r)

t = 2pi*r/v. You can only keep one of the three variables constant.
2012
Mathematical Methods (50) Chinese SL (45~52)

2013
English Language (50) Chemistry (50) Specialist Mathematics (49~54.9) Physics (49) UMEP Physics (96%) ATAR 99.95

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Alwin

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Re: VCE Physics Question Thread!
« Reply #137 on: August 25, 2013, 06:09:41 pm »
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I'm just a more outspoken member of the "dissatisfied with VCE" group. There are heaps of people like me. They just don't want to be so vocal for fear of offending people.
...
lol well, I spent too much on maths in earlier life. Parabolas was year five for me. I still remember fumbling around to understand what this f(-b/2a) meant in primary school.

with him on this^
I just cbbs ranting here + its a question thread not a bagging thread ;) (I just +1 him everytime ;) )
I'll just add for me parabolas in grade 3.  as for the  f(-b/2a) i 'proved' it by taking the mean of the two intercepts that can be found by the quadratic formula. Then proved it a couple years later with calculus, which is SO hard on physics... esp since on some exams they don't even bother to draw graphs correctly since we can count the squares XD

anyways:
Determine a relationship between F and m so everything else must be kept constant. Think about how best to keep v^2/r constant while collecting your f vs m data.
Thanks, so i will select a time to make the period for every test i do and also raidus.. however do you know how i would go about keeping period the same w/o increasing speed (because it increases my r)

you want it to increase your r..  say k=v^2/r, so when v increase you need r to increase (at a rate proportional to the square of the increase of v). Otherwise, v increases r stays same  -> k increases (ie not constant = fail).

BUT you are testing the relationship between F and m. So, you want to keep everything else (r, T, v etc) constant.

you change the mass...
« Last Edit: August 25, 2013, 06:41:25 pm by Alwin »
2012:  Methods [48] Physics [49]
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lzxnl

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Re: VCE Physics Question Thread!
« Reply #138 on: August 25, 2013, 06:36:13 pm »
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To be honest, I had no idea what he wanted, as simply investigating the relationship between F and m is...trivial. F = ma arises from a definition of force in Newtonian mechanics and with a constant mass. So why would anyone measure the relationship between F and m? It's just measuring your experimental capabilities.
2012
Mathematical Methods (50) Chinese SL (45~52)

2013
English Language (50) Chemistry (50) Specialist Mathematics (49~54.9) Physics (49) UMEP Physics (96%) ATAR 99.95

2014-2016: University of Melbourne, Bachelor of Science, Diploma in Mathematical Sciences (Applied Maths)

2017-2018: Master of Science (Applied Mathematics)

2019-2024: PhD, MIT (Applied Mathematics)

Accepting students for VCE tutoring in Maths Methods, Specialist Maths and Physics! (and university maths/physics too) PM for more details

Alwin

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Re: VCE Physics Question Thread!
« Reply #139 on: August 25, 2013, 06:46:45 pm »
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To be honest, I had no idea what he wanted, as simply investigating the relationship between F and m is...trivial. F = ma arises from a definition of force in Newtonian mechanics and with a constant mass. So why would anyone measure the relationship between F and m? It's just measuring your experimental capabilities.

its not like vce physics would test maths skills :P

I've given it some thought, sydneyboy, and i think i have an idea of what your prac is testing: try different masses and plot a graph of F vs m?? It should be straight line since when  v^2/r constant F ∝ m. If it's not straight, then you talk about errors like not keeping v^2/r constant...
Is this interpretation right?

Otherwise just post the prac sheet and we (esp nliu since he <3 vce physics :P ) will do our best to try help!! Or, ask your teacher for clarification.

EDIT (in spoiler):
SECRET TO SUCCEEDING IN ANY PRAC
Just copy what the smart people in your class are doing :P  Or worse comes to worse make up/tweak your data results after the prac then write some cohesive BS about errors and stuff :D
Or just blame the teacher hahahaha. that always goes down well..
« Last Edit: August 31, 2013, 09:06:21 pm by Alwin »
2012:  Methods [48] Physics [49]
2013:  English [40] (oops) Chemistry [46] Spesh [42] Indo SL [34] Uni Maths: Melb UMEP [4.5] Monash MUEP [just for a bit of fun]
2014:  BAeroEng/BComm

A pessimist says a glass is half empty, an optimist says a glass is half full.
An engineer says the glass has a safety factor of 2.0

lolipopper

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Re: VCE Physics Question Thread!
« Reply #140 on: August 25, 2013, 08:22:11 pm »
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question: how do i link the generation of AC EMF to its use in a DC motor.
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sydneyboy

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Re: VCE Physics Question Thread!
« Reply #141 on: August 25, 2013, 08:49:06 pm »
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hey guys thinks for all the replies, there was a part A which explored relationship between Tension and V^2 - this was worth 80% of the marks. This next section is worth 20% and is the 'challenge' part of the sac so all we were given is

"Given Fnet = mv^2/r
Determine a relationship between F and m so everything else must be kept constant. Think about how best to keep v^2/r constant while collecting your f vs m data.
Clue: what is another way of expressing v^2/r and how can this be kept constant even when radius is changing." on  a piece of paper.

@Alwin im sure your interpretation is right. I have 2 periods left to record data and plot the graph. I think it will be a tedious task to make everything constant.

Thanks for the help guys I'll have a crack tomorrow i have a much better idea of what to do now.

SocialRhubarb

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Re: VCE Physics Question Thread!
« Reply #142 on: August 25, 2013, 09:34:56 pm »
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This is late but:

It might help to know what equipment you've been given.

But honestly, I have no idea how to approach this. Obviously you want to keep v^2/r constant, but I suppose the question is how can you best do it, so as to minimise the error in your results. Especially since it's telling you to keep it constant "even when radius is changing".

My first thought was to swing it in a vertical arc, and then use gravity to kind of 'calibrate' your v^2/r value, but that really presents more problems than solutions, especially if you're swinging your mass by hand.

I suppose I'll have to go with what everyone else is saying and just say "keep the period and radius constant" even though it's not really answering the question of how to keep v^2/r constant with a changing radius.
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sydneyboy

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Re: VCE Physics Question Thread!
« Reply #143 on: August 25, 2013, 09:43:13 pm »
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sydneyboy

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Re: VCE Physics Question Thread!
« Reply #144 on: August 25, 2013, 09:44:28 pm »
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There is a speed setting on it

lolipopper

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Re: VCE Physics Question Thread!
« Reply #145 on: August 27, 2013, 11:53:27 pm »
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in circuit construction questions how do you know where the switching circuit goes?
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Lasercookie

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Re: VCE Physics Question Thread!
« Reply #146 on: August 28, 2013, 04:10:34 pm »
+1
EDIT (in spoiler):
SECRET TO SUCCEEDING IN ANY PRAC
Just copy what the smart people in your class are doing :P  Or worse comes to worse make up/tweak your data results after the prac then write some cohesive BS about errors and stuff :D
Or just blame the teacher hahahaha. that always goes down well..
I'm guessing you meant it tongue in cheek, but anyway :P it depends if your teacher is expecting you to get the correct results from the experiment though, a well designed practical sac would allow you to still do pretty well if you're able to explain how your data turned out to be messed up.

lolipopper

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Re: VCE Physics Question Thread!
« Reply #147 on: September 02, 2013, 08:00:09 pm »
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question :

A proton and electron are accelerated from rest through the same potential difference. Given that their masses are in a ratio of 1836:1 , find the ratio of their de Broglie wavelengths.
« Last Edit: September 02, 2013, 08:06:27 pm by lolipopper »
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SocialRhubarb

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Re: VCE Physics Question Thread!
« Reply #148 on: September 02, 2013, 08:14:50 pm »
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Okay. Firstly, the magnitude of charge on the electron is the same as the magnitude of the charge on the proton. This means that accelerating them through the same potential difference gives them the same energy, since potential difference is energy per charge. Let's use the subscript 'p' for the proton, and the subscript 'e' for the electron.







Using the formulas for momentum and energy of a particle, ,     we can easily derive a relationship between the two.





, substituting in our two pieces of information from before.



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saifh

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Re: VCE Physics Question Thread!
« Reply #149 on: September 02, 2013, 10:06:18 pm »
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A question I need answered :)

1. Describe the photoelectric effect's implications for the wave model of light and how it forced the reintroduction of a particle model or photon model for light