General Thoughts: Physics (1 Viewer)

darkchild69

Nanotechnologist
Guys, i just noticed the paper which I have got my hands on is missing Q25 and 26!

What were these questions?

I remember seeing this somewhere, i must have lost it..

untouchablecuz

Active Member
er

for b)

i did this:

T=d/v

d=720 lightyears = (c * 365 * 24 * 60 * 60) m

v= 0.9999c m/s

T=31536315.36 s=1.001y

: S

wheres the flaw

EDIT: OMG I DIDNT MULTIPLY (c * 365 * 24 * 60 * 60) m BY 720 OMG

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tonyharrison

Member
I did...but my answer looks scarily similar to yours *cry*

rorycole92

New Member
For that light year question, calculate the time taken did anyone get something lyk this : 2.396x10^10 seconds?
Yeah i think thats what i got... hope its right lol

shaon0

...
Yeah i think thats what i got... hope its right lol
Not really, i think i got 2.46*10^15 seconds. But i'm sure i got it wrong.

electrolysis

congenital schmuck
lol i'm really late to this thread...
BUT WHAT A FREAKING AWESOME EXAM <33

Definitely the exam that I felt most confident leaving out of the exam hall so far (even better than chem )

Must've been all the physics pick up lines in the 'Physics Marathon 2009' thread

whitnall8

Member
With the torque question with the load of 40 g and needing to find B, was the torque only on half of the coil, or on the entire coil?

In T = BIA, was B 0.3 x 0.1 or 0.6 x 0.1

abhi23

Coming to the Toga Party?
Best exam ever. But kinda feels like a lot of the theory learning went to waste.
Can't complain though. It's all over!!!

Cloesd

Member
Re: 2009 HSC Physics - How did you go?

i think ure looking too much into the question, i think their looking for u to say that g cant be sheilded, hence C is correct
I think that question will be removed or something. Since when did the BOS punish looking overly into the question? (although you could answer that question with, since always)

For the Germanium-silicon one.. I put down C. Silicon is more abundant.

Source: Materials for high-temperature ... - Google Books

First few lines

"Silicon is the dominant semiconductor material in use by the electronics industry, but it is generally not thought of as a high-temperature semiconductor material, it's narrow energy gap creates the majority of problems during high temperature operation"

I think i read somewhere (in an electrical engineering book), Silicon semiconductor P-N junctions let through roughly double the amount of current in a reverse bias (the wrong way) for every 10 degrees the heat increases.

No idea what Germanium's values are though.

That said, i have seen sources advocating i am incorrect... ie: http://www.ecse.rpi.edu/~schubert/Course-Teaching-modules/A27-Silicon-versus-germanium---A-historical-perspective.pdf

hmm teaching course modules..
maybe the entire education industry in terms of silicon vs germanium is sabotaged.

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Cloesd

Member
Re: 2009 HSC Physics - How did you go?

It is NOT correct as the work done is from infinity to those points. In that answer the assumption is horses for courses and could possible refer to zero as the centre of earth.

Either way whoever wrote those answers has no clue how to write proper English. The real answer is the a bit of C and a bit of D as C has the word "difference" stated the correct part but fails to mention from infinity... whilst D states a very large distance away but fails to mention geosynchronous and difference.

What a crap of a question... and then A comes in and possibly based on correct terminology could be the BEST answer... LOL but C and D is where it should have been.... arghhhhhhhhhhhh :burn:

AMBIGUOUS MC answers NSW BOS - PHYSICISTS SAY NO!!!!!

I still believe its C.

A cannot possibly be correct, gravitational potential energy is 0 at infinite and negative as we get closer to the planet. Thus to move from a lower orbit, to a higher orbit.. our GPE would go from a VERY negative figure, to a slightly less negative figure.. essentially it is increasing

B cannot be the answer, for the CHANGE in gravitational potential energy is not dependant on the mass. It is based soley on the distance from the planet.

C makes the most sense, I have actually DONE a question that asked "A satelite is in a 20,000km orbit around a planet, and moves to an 80,000 one, what was the work done in order to achieve this? It was the difference in gravitational potential energy.

D Neglects the first orbit completely, how can the work done neglect the first orbit? that would imply many false things like.. Dragging an object half way across the universe from a mass, takes no "work" at all. And all kinds of ridiculous outcomes would sprout, if D was correct.

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Cloesd

Member
Re: 2009 HSC Physics - How did you go?

i got

1.C
2.A
3.C
4.D
5.C
6.A
7.C
8.C
9.A
10.B
11.D
12.D
13.B
14.C
15.A

I think this is pretty much correct, except for 9, which i cannot confirm.

The question came up before, but was very confusing.... If there is a rod and there is a velocity moving this rod in the downard direction... does that mean force is down ...

OR does that mean the force is generated that opposes the direction of movement, thus the force is up...

Continuum

I'm squishy
Re: 2009 HSC Physics - How did you go?

its a concept question which i put down c first as well but i changed it due to the hard fact i thought of in my mind. consider the case where no earth exist. the force would b only caused due to gravitational attraction. now u put earth in the middle. if c was 2 b correct then ur saying earth does not apply a force on either sun or the moon as the force is constant and hence ur saying newton's theory is totally wrong. so ur basically challenging newton, the greatest sciencest ever and his work. if u still want to say c is correct then u have 2 abolish the whole newtonian physics and it will mean sun would not exert a force on the moon in the first place. if bos said c was the correct answer then i would simply ask them r they saying newton is wrong coz it comes down to tat matter. (and yea i'm a freak at physics) (though newton was abit wrong at his law of universal gravitation but tats only if u take in extremities which is explained by einstein and his general relativity in uni which i have already learnt and i'm yr 12 just 2 make things clear)
earth does apply a force on both the sun and the moon and in doing so, changes the NET force experienced by either bodies respectively. however, the force that the sun exerts on the moon and vice versa, does not change - it will always be the same value as determined (or approximated if you wanna be a dickhead or pedantic about it) by newton's law of gravitation. it does not void any theory at all.

you call yourself a physics freak and yet you didn't see this? lolfuckinglol.

clonestar

Physicist/*******
I must say looking back at this paper still the BOS creates questions with are ambiguous...

In any case when a q raises doubt get rid of it....
I mean seriously when will they learn and I still argue that Q3 is D as the gravitational field can be implied as the geosynchronous orbit and the exact definition of work done is correct to state from infinity or a very large distance away to those two orbital location and working out the difference.

Cloesd.....Option C has no reference to the infinity point so could imply the centre of the Earth and is too ambiguous in nature...each to their own and it could be argued both ways. A and B are both wrong.

I am absolutely certain they(BOS) will choose C and this is what I initially thought as the answer until I looked at D though D has more loose ends and has 2 missing key words(difference) and (geosynchrous orbit)...but then again C is also msisign l;arge distance away or infinity which is how your calculate the work done.... FFS are we analysing answers based on English or Physics principles

HATE!!! HATE !!! HATE!!!!

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clonestar

Physicist/*******
In that particular question you guys are talking about, it is definately t0, as it is YOUR frame of reference and relative to YOU it is not moving at velocity (hence t0)

Essentially the answer should have come out to be

tv = 170,001.70 years (t = d/s)

t0 = tv (1-(v^2/c^2))^1/2

t0 = 170,001.70(1-(0.99999^2)^1/2

t0 = 760.27y
This is what I got too 760.26light years away...

clonestar

Physicist/*******
With Q19

the electron projectile can anyone confirm this was correct?

a)
F=qE
= 1.602 x 10^19 x V/d = 100/0.1
= 1.6 x 10^-16N downwards

b)
Electric force = Newtons Force
qE(a) = ma
1.6 x 10^-16 = 9.1 x 10^-31 x a
a= 1.758 x 10^14m/s^2

so now use projectile motion analysis
Vy=Uy + at
0=5.2 x 10^6 + -1.758 x 10^14 x t
t= 2.955 x 10^-8s

Therefore x 2 for second section

and t= 5.91 x 10^-8seconds

Can anyone confirm this is what they got for Q19?

Cheers...

ALSO- I HAVE NOT SEEN A SPECTROMETER have an electric field(alone) usually it is combined with a magnetic field in the first section and then a pure mag field for the important part(mass deflection/calculation). How can they say for part a) the force experienced by the electron inside the spectrometer when the spectrometer itself should be either a magnetic field/electric field or the second part which is a magnetic field not an electric field alone??? there is no spectrometer that i know of that has the electric field all by itself????

Usually if not all SPECTROMETER have a magnetic field and electric field at the start in which the electrons/protons/ions enter undeflected and then it enters a second stronger magnetic field where using RHR the curve is analysed (radius) to obtain the mass??. Anyone else find this an odd question and NOT CORRECT Physics???? I think I will ask them for further clarification...

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bront

New Member
how did everyone calculate accelleration for the projectile?
due to electric feild strength?

bront

New Member
cant remember what i got for q19 but i calculated accelleration using f=ma then calculating force due to electric field strength then doing projectile
it was like0.000012 secs

whitnall8

Member
I got 5.9 x 10^-8 (s) as well for the projectile motion question as well doing pretty much what you did

00iCon

Member
waaaaaay too many equations
the board of studies is getting Jewish
equations are easier and cheaper to mark then reponses so there taking the easy way out and not testing students as they should be. ie on the theory
aside from that i didnt think it was too bad
just pissed off expecting to get asked questions to explain and discuss physics theory and ended up sitting a math exam
If they were REALLY Jewish, they'd make it all multiple choice, and computer marked. LOL at the American SAT...

clonestar

Physicist/*******
Just an update for Q3 and why I think it's D.

Check out the outcome on Pg 41 of the syllabus. It states:

"Define Gravitational potential energy as the work done to move an object from a very large distance away to a point in a gravitational field"

If you take the NSW BOS syllabus outcome and link it with Q3 MC 2009 PHYSICS HSC the answer is parallel to this:

"the work done is the energy required to move the satellite which is in a gravitational field, from a very large distance away, to the higher orbit.

This statement correctly identifies the large distance away and also correctly identifies the gravitational field as the geosynchronous orbit.

If they choose C as the correct answer then the outcome should be scraped and re-written removing the large distance away and including the difference which is already assumed in choice D.