Login

Welcome, Guest. Please login or register.

March 29, 2024, 08:54:47 am

Author Topic: VCE Physics Question Thread!  (Read 603381 times)  Share 

0 Members and 1 Guest are viewing this topic.

Einstein

  • Guest
Re: VCE Physics Question Thread!
« Reply #465 on: June 04, 2014, 06:13:30 pm »
0
how and what is the answer to this question, from electricity sac.

Thanks

b^3

  • Honorary Moderator
  • ATAR Notes Legend
  • *******
  • Posts: 3529
  • Overloading, just don't do it.
  • Respect: +631
  • School: Western Suburbs Area
  • School Grad Year: 2011
Re: VCE Physics Question Thread!
« Reply #466 on: June 04, 2014, 06:20:43 pm »
+3
how and what is the answer to this question, from electricity sac.

Thanks
They need to be a multiple of the elementary charge, which is approximately (I can't remember how many sig figs you do it to in physics but it doesn't matter here).
So if you divide each of the charges by the elementarycharge, you should get an integer.
Doing this gives
A. 20
B. 5
C. 37.5
D. 90

So option C is the only one that isn't an integer multiple of the elementary charge, and so that charge could not exist. i.e. Option C.
« Last Edit: June 04, 2014, 06:22:32 pm by b^3 »
2012-2016: Aerospace Engineering/Science (Double Major in Applied Mathematics - Monash Uni)
TI-NSPIRE GUIDES: METH, SPESH

Co-Authored AtarNotes' Maths Study Guides


I'm starting to get too old for this... May be on here or irc from time to time.

Einstein

  • Guest
Re: VCE Physics Question Thread!
« Reply #467 on: June 04, 2014, 07:23:57 pm »
0
how is this derived?

RKTR

  • Victorian
  • Forum Leader
  • ****
  • Posts: 613
  • Respect: +17
Re: VCE Physics Question Thread!
« Reply #468 on: June 04, 2014, 11:11:06 pm »
0
how is this derived?
already forgot about this. had to refer to my year 11 textbook. Sv is the unit for dose equivalent while Gy is the unit for absorbed dose.
the symbol before the Sv and Gy is micro which is 10^-6 . To determine the most damaging, you have to convert all them to dose equivalent. dose equivalent = absorbed dose x quality factor.
A 20 x 10^-6
B 30 x 10^-6 x (1) =30 x 10^-6
C 30 x 10^-6
D 20 x 10^-6  x( quality factor of 10-20) =(200  to 400) x 10^-6

dose equivalent of D is highest so it is the most damaging.
2015-2017: Bachelor of Biomedicine (Neuroscience)
2018: Doctor of Medicine (Withdrawn)
2019: Bachelor of Commerce (Actuarial Studies?)

Stew_822

  • Victorian
  • Forum Regular
  • **
  • Posts: 60
  • Respect: 0
Re: VCE Physics Question Thread!
« Reply #469 on: June 14, 2014, 12:33:28 pm »
0
Hi guys,

I'm really stuck with a voltage divider question, I thought I had them down but this one is confusing me.

It's question 32 and 33 of A+ Notes for physics.

I realise the photo isn't clear - Change in Vout = 6V and change in Vin = 0.4V

So here's the answers from the book and my answers afterwards:
Answer to Q30 is 0.6V and 4V - no worries.
Answer to Q31 is 15V - wtf? Isn't it negative 15V because the amplifier is inverting?
Answer to Q32 is 2.5V - That's reading from the graph but when you do Vout = Vgain * Vin = -15 * 0.7 = 10.5V, it doesn't agree with the graph. Can anyone explain why this is the case?
Answer to Q33 is 5.5V - Same problem as Q32.

Thanks,
Stewart
« Last Edit: June 14, 2014, 01:06:16 pm by Stew_822 »
"It's better to keep your mouth shut and give the impression you're stupid than to open it and remove all doubt."

speedy

  • Victorian
  • Forum Obsessive
  • ***
  • Posts: 336
  • Respect: 0
  • School Grad Year: 2014
Re: VCE Physics Question Thread!
« Reply #470 on: June 14, 2014, 05:30:43 pm »
+1
Hi guys,

I'm really stuck with a voltage divider question, I thought I had them down but this one is confusing me.

It's question 32 and 33 of A+ Notes for physics.

I realise the photo isn't clear - Change in Vout = 6V and change in Vin = 0.4V

So here's the answers from the book and my answers afterwards:
Answer to Q30 is 0.6V and 4V - no worries.
Answer to Q31 is 15V - wtf? Isn't it negative 15V because the amplifier is inverting?
Answer to Q32 is 2.5V - That's reading from the graph but when you do Vout = Vgain * Vin = -15 * 0.7 = 10.5V, it doesn't agree with the graph. Can anyone explain why this is the case?
Answer to Q33 is 5.5V - Same problem as Q32.

Thanks,
Stewart

Gain is an absolute value and is usually given as positive regardless of it inverting or not. However the assessors accept either positive or negative values.

What you must realise is that this amplifier is biased - its transfer characteristics graph doesn't pass through the origin. When you simply multiply Vin by the gain, you are treating the amplifier as if it is unbiased. To take the biasing into account, the graph must be used.
Physics [50] | Chemistry [45] | English [42] | IT:SD [44]
ATAR: 98.95

Stew_822

  • Victorian
  • Forum Regular
  • **
  • Posts: 60
  • Respect: 0
Re: VCE Physics Question Thread!
« Reply #471 on: June 14, 2014, 09:55:46 pm »
0
Ah, I see - I didn't realise there was a difference (or more to the point didn't realise it made a difference). The Heinemann textbook only seems to contain non-biased amplifiers, lucky then that I got these questions now rather than in an exam.

Is that the only way you can find V_out, by reading it off the graph? Or is there a mathematical method also that takes into account the biased nature of the amplifier. Final question, if there is a mathematical method do I need to know it or will the graph be given in the exam?

Many thanks for your help,
Stewart
"It's better to keep your mouth shut and give the impression you're stupid than to open it and remove all doubt."

Rishi97

  • Victorian
  • Part of the furniture
  • *****
  • Posts: 1042
  • Respect: +40
  • School: The University of Melbourne
  • School Grad Year: 2014
Re: VCE Physics Question Thread!
« Reply #472 on: June 21, 2014, 12:01:24 pm »
0
Power lines carry an electric current in the Earth's magnetic field. Which would experience the greater magnetic force: a north-south power line or an east-west power line? Explain
Many thanks :)
2014: VCE completed
2015-2017: BSc at Melb Uni

DREAM, BELIEVE, ACHIEVE!!!

lzxnl

  • Victorian
  • ATAR Notes Legend
  • *******
  • Posts: 3432
  • Respect: +215
Re: VCE Physics Question Thread!
« Reply #473 on: June 21, 2014, 06:52:22 pm »
+1
Earth's magnetic field runs south to north (at least along the Earth's surface), so any current parallel or antiparallel to this would experience no force. Hence your power line needs to be east-west for there to be a force.
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

Orb

  • Part of the furniture
  • *****
  • Posts: 1649
  • Respect: +426
Re: VCE Physics Question Thread!
« Reply #474 on: June 23, 2014, 01:35:28 pm »
0
When we're calculating the co-efficient of friction, formula Fr= m x N
where m is the co-efficient of friction,

What unit do we attribute to N, the normal reaction force? Do we use the mass provided or do we convert it into newtons?
45+ raw score guaranteed (or 100% refund) for 2022 Methods & Specialist (other subjects also available - classes for all) register now!

Also hiring excellent Methods, Chemistry, Physics, Biology + Specialist tutors with a passion for excellence - PM me!

We also now support Chemistry, Physics and Biology!

Jacyan

  • Victorian
  • Adventurer
  • *
  • Posts: 10
  • Respect: +1
  • School Grad Year: 2013
Re: VCE Physics Question Thread!
« Reply #475 on: June 23, 2014, 02:01:23 pm »
+1
When we're calculating the co-efficient of friction, formula Fr= m x N
where m is the co-efficient of friction,

What unit do we attribute to N, the normal reaction force? Do we use the mass provided or do we convert it into newtons?

Fr is in newtons, N is in newtons, and the co-efficient of friction has no units.
2014 - 2016: Bachelor of Commerce Scholars Program [Actuary]

Orb

  • Part of the furniture
  • *****
  • Posts: 1649
  • Respect: +426
Re: VCE Physics Question Thread!
« Reply #476 on: June 23, 2014, 02:07:12 pm »
0
So how should I approach this question...

I get a result that's 10x more than the actual answer :/
45+ raw score guaranteed (or 100% refund) for 2022 Methods & Specialist (other subjects also available - classes for all) register now!

Also hiring excellent Methods, Chemistry, Physics, Biology + Specialist tutors with a passion for excellence - PM me!

We also now support Chemistry, Physics and Biology!

Ancora_Imparo

  • Victorian
  • Trendsetter
  • **
  • Posts: 105
  • Respect: +32
Re: VCE Physics Question Thread!
« Reply #477 on: June 23, 2014, 07:17:31 pm »
+1
So how should I approach this question...

I get a result that's 10x more than the actual answer :/

As we are told the system is moving left, let left be positive. Let the tension in the left rope be and the tension in the right rope be .

Draw the forces the acting on each block.
For M1: mg is down and T1 is up
For M2: mg is down, N is up, T1 is left, T2 is right, friction is right (as we are told block is moving to the left)
For M3: mg is down, T2 is up

Since acceleration of whole system is the same, we can apply Newton's second law to each block individually.
For M1:

--- Eq. 1

For M2:
You also know that
Thus:

--- Eq. 2

For M3:

--- Eq. 3

Adding Eq. 1 and Eq 3. gives:
--- Eq. 4

Adding Eq. 2 and Eq 4. gives:

[EDIT: Whoops, got the fraction the wrong way around the first time]
(negative sign shows that it's decelerating)

Hope that helps.
« Last Edit: June 24, 2014, 12:07:05 pm by Ancora_Imparo »
VCE TUTOR FOR BIOLOGY, CHEMISTRY, MATHEMATICAL METHODS (CAS), PHYSICS & SPECIALIST MATHEMATICS. TUTORING AT GLEN WAVERLEY LIBRARY OR MONASH UNIVERSITY, CLAYTON. PM ME IF INTERESTED.

Orb

  • Part of the furniture
  • *****
  • Posts: 1649
  • Respect: +426
Re: VCE Physics Question Thread!
« Reply #478 on: June 24, 2014, 10:32:47 am »
0
As we are told the system is moving left, let left be positive. Let the tension in the left rope be and the tension in the right rope be .

Draw the forces the acting on each block.
For M1: mg is down and T1 is up
For M2: mg is down, N is up, T1 is left, T2 is right, friction is right (as we are told block is moving to the left)
For M3: mg is down, T2 is up

Since acceleration of whole system is the same, we can apply Newton's second law to each block individually.
For M1:

--- Eq. 1

For M2:
You also know that
Thus:

--- Eq. 2

For M3:

--- Eq. 3

Adding Eq. 1 and Eq 3. gives:
--- Eq. 4

Adding Eq. 2 and Eq 4. gives:

(negative sign shows that it's decelerating)

Hope that helps.

I'm sorry, i'm not sure what you did wrong but apparently that wasn't what the answer is...

Solution for the question was 5.6 ms ^-2

45+ raw score guaranteed (or 100% refund) for 2022 Methods & Specialist (other subjects also available - classes for all) register now!

Also hiring excellent Methods, Chemistry, Physics, Biology + Specialist tutors with a passion for excellence - PM me!

We also now support Chemistry, Physics and Biology!

Zealous

  • ATAR Notes Lecturer
  • Victorian
  • Forum Leader
  • ****
  • Posts: 889
  • zeal: great enthusiasm in pursuit of an objective.
  • Respect: +242
Re: VCE Physics Question Thread!
« Reply #479 on: June 24, 2014, 11:01:53 am »
0
I'm sorry, i'm not sure what you did wrong but apparently that wasn't what the answer is...

Solution for the question was 5.6 ms ^-2
I'll give this a shot. Hopefully my explanation makes sense.

First let's look at the forces due to gravity. We have a force due to gravity of M3 which is and the force due to gravity on M1 which is .

Now let's consider the frictional force of M2:




Friction acts against a motion, so since M2 was initially moving left, the force of friction will be acting in the right/clockwise direction.

If we consider moving right/clockwise to be positive, the sum of the forces will be:

M3 and M2 are causing the system to move right so they are positive, and M1 is working against both of them so is negative.

Hence:


vce:
2013: Further [50] (+Premier's) | Methods [48]
2014: Physics [50] | Specialist | Accounting | English Language || ATAR: 99.70 + Australian Student Prize!
uni:
2015: Bachelor of Commerce and Engineering (Honours)