Login

Welcome, Guest. Please login or register.

March 29, 2024, 01:25:24 am

Author Topic: VCE Physics Question Thread!  (Read 603246 times)  Share 

0 Members and 3 Guests are viewing this topic.

lzxnl

  • Victorian
  • ATAR Notes Legend
  • *******
  • Posts: 3432
  • Respect: +215
Re: VCE Physics Question Thread!
« Reply #45 on: May 29, 2013, 04:17:40 pm »
0
1. RMS means root-mean-square. It really should be called "square-mean-root" as you square your function, average it and then square root it. Why do we need it? AC voltage is sinusoidally varying; its average value over a cycle is zero. That's not very useful. However, in power calculations, where P=V^2/R, an average of V^2 is just as good. This time, if we square the voltage, it's always positive and now an average makes sense. I won't go into the calculation details, but the RMS voltage is the peak voltage divided by sqrt 2, for a sinusoidal wave only (which is VCE physics). Just know how to calculate RMS voltages, currents, what they mean and the fact that P=I^2 R or V^2/R refers to RMS currents and voltages.

2. If a photodiode is forward-biased, it is a regular diode. Only when reverse-biased does its behaviour depend on light like in the course. Then, the photocurrent is directly proportional to the intensity of light striking the diode. If the light intensity doubles, the current doubles.

3. I'm not great with transistors, sorry. My electronics knowledge is strictly limited to what's in the course.
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

Robert123

  • Victorian
  • Forum Obsessive
  • ***
  • Posts: 201
  • Respect: +5
  • School: Kyabram P-12 College
Re: VCE Physics Question Thread!
« Reply #46 on: May 29, 2013, 07:13:22 pm »
0



Thanks for that, I had questions on those topics for a practice SAC and our class haven't cover much of this stuff in detail if at all.
Another question relating to springs.
Pinball game has a ball with mass 0.15kg which is launch by a compressed spring at 4.2m/s that has been compressed by 20 cm. If the spring is "ideal" what is the spring constant k in N/m?
Since k is N/m, would you use constant acceleration formulas to find the acceleration, multiply it by mass (since F=ma) and divide by distance (k=F/x)? Would you have to worry about the constant acceleration question or are you meant to substitute the final speed for acceleration?

availn

  • Victorian
  • Forum Obsessive
  • ***
  • Posts: 250
  • Respect: +13
  • School Grad Year: 2013
Re: VCE Physics Question Thread!
« Reply #47 on: May 29, 2013, 08:02:17 pm »
0
Thanks for that, I had questions on those topics for a practice SAC and our class haven't cover much of this stuff in detail if at all.
Another question relating to springs.
Pinball game has a ball with mass 0.15kg which is launch by a compressed spring at 4.2m/s that has been compressed by 20 cm. If the spring is "ideal" what is the spring constant k in N/m?
Since k is N/m, would you use constant acceleration formulas to find the acceleration, multiply it by mass (since F=ma) and divide by distance (k=F/x)? Would you have to worry about the constant acceleration question or are you meant to substitute the final speed for acceleration?

You cannot do this easily with kinematics, because a spring does not accelerate a mass at a constant rate. You should do this with energy, spring potential energy before equals kinetic energy after.

0.5kx2 = 0.5mv2
k · 0.22 = 0.15 · 4.22
∴ k = 66.15Nm-1
2011: Software Development (43)
2012: Methods (41), Physics (45)
2013: Literature (38), German (35), Specialist (39), Accounting (40), UMEP Physics (4.5)
ATAR: 98.65

random_person

  • Victorian
  • Trendsetter
  • **
  • Posts: 116
  • Respect: +5
Re: VCE Physics Question Thread!
« Reply #48 on: May 29, 2013, 08:04:22 pm »
0
Thanks for that, I had questions on those topics for a practice SAC and our class haven't cover much of this stuff in detail if at all.
Another question relating to springs.
Pinball game has a ball with mass 0.15kg which is launch by a compressed spring at 4.2m/s that has been compressed by 20 cm. If the spring is "ideal" what is the spring constant k in N/m?
Since k is N/m, would you use constant acceleration formulas to find the acceleration, multiply it by mass (since F=ma) and divide by distance (k=F/x)? Would you have to worry about the constant acceleration question or are you meant to substitute the final speed for acceleration?

We have m=0.15kg, v=4.2ms-1, s=20cm=0.2m

EK=1/2 mv2
=1/2 0.15 x 4.22
=1.323 J
Us=1/2 ks2
therefore
1.323=1/2 k x 0.22
k=66.15Nm-1

Hope this helps


2012: Further Mathematics [50] (Premier's Award)
2013: English | Physics | Mathematical Methods | Specialist Mathematics | Chemistry
Bachelor of Medicine/Bachelor of Surgery (Honours)

PM me any questions about the UMAT and Monash Medicine!

Sentar

  • Victorian
  • Adventurer
  • *
  • Posts: 19
  • Respect: 0
  • School: Marcellin College
  • School Grad Year: 2013
Re: VCE Physics Question Thread!
« Reply #49 on: June 03, 2013, 04:01:23 pm »
0
Found an exam question but can't find the answer anywhere, don't have the actual answers, seeing if anyone can help.

Explain how it is possible to transmit the information contained in an electrical signal which has both a positive and negative component, when it is impossible to produce a beam of light with negative intensity?

Cheers
2012: Maths Methods (43), Religion and Society (30)
2013: English language, Chemistry, Physics, Specialist Maths

lzxnl

  • Victorian
  • ATAR Notes Legend
  • *******
  • Posts: 3432
  • Respect: +215
Re: VCE Physics Question Thread!
« Reply #50 on: June 03, 2013, 04:29:53 pm »
0
You just need a light signal whose amplitude varies just like your electrical signal/has the same shape. E.g. move the electrical signal up so it's always positive.
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

~T

  • Victorian
  • Trendsetter
  • **
  • Posts: 197
  • Respect: +4
  • School: St Patrick's College
  • School Grad Year: 2013
Re: VCE Physics Question Thread!
« Reply #51 on: June 10, 2013, 11:19:35 pm »
0
Just looking at the 2012 Exam 2 paper and confused with question 1. Basically, there is a point P and it asks for you to draw an arrow at P indicating the direction of the magnetic field. There is a solenoid which will produce a field (comparable to Earth's) going right, and there is an arrow pointing upwards that says "magnetic north."

The answers say that the arrow drawn should be "to the right and up the page at an angle of approximately 45°." However, in saying that "magnetic north" is upwards, does that not mean that the field lines due to the Earth should be going downwards? If magnetic north is up, magnetic south is down, and field lines go from north to south. I would have drawn an arrow "to the right and *DOWN* the page at an angle of approximately 45°."

Basically, in saying that magnetic north is up, does that not mean that geographical north is downwards?
ATAR: 99.95
Specialist 50 | Methods 50 | Physics 50 | Further 49 | Literature 48 | Music Style/Composition 41

2014 - 2016: Bachelor of Science (Chancellor's Scholars' Program) at The University of Melbourne

I will be tutoring in Melbourne this year. Methods, Specialist, and Physics. PM me if you are interested :)

availn

  • Victorian
  • Forum Obsessive
  • ***
  • Posts: 250
  • Respect: +13
  • School Grad Year: 2013
Re: VCE Physics Question Thread!
« Reply #52 on: June 11, 2013, 02:18:50 pm »
0
Just looking at the 2012 Exam 2 paper and confused with question 1. Basically, there is a point P and it asks for you to draw an arrow at P indicating the direction of the magnetic field. There is a solenoid which will produce a field (comparable to Earth's) going right, and there is an arrow pointing upwards that says "magnetic north."

The answers say that the arrow drawn should be "to the right and up the page at an angle of approximately 45°." However, in saying that "magnetic north" is upwards, does that not mean that the field lines due to the Earth should be going downwards? If magnetic north is up, magnetic south is down, and field lines go from north to south. I would have drawn an arrow "to the right and *DOWN* the page at an angle of approximately 45°."

Basically, in saying that magnetic north is up, does that not mean that geographical north is downwards?

Nope. My friend got hit by this too.

Magnetic North and North Magnetic Pole is at the earth's north.
Magnetic North Pole is at the earth's south.
2011: Software Development (43)
2012: Methods (41), Physics (45)
2013: Literature (38), German (35), Specialist (39), Accounting (40), UMEP Physics (4.5)
ATAR: 98.65

~T

  • Victorian
  • Trendsetter
  • **
  • Posts: 197
  • Respect: +4
  • School: St Patrick's College
  • School Grad Year: 2013
Re: VCE Physics Question Thread!
« Reply #53 on: June 12, 2013, 06:19:45 pm »
0
Oh really? So magnetic north is actually a south pole (in dipole terms)? No wonder >50% got that wrong.
ATAR: 99.95
Specialist 50 | Methods 50 | Physics 50 | Further 49 | Literature 48 | Music Style/Composition 41

2014 - 2016: Bachelor of Science (Chancellor's Scholars' Program) at The University of Melbourne

I will be tutoring in Melbourne this year. Methods, Specialist, and Physics. PM me if you are interested :)

jono88

  • Victorian
  • Trendsetter
  • **
  • Posts: 104
  • Respect: 0
Re: VCE Physics Question Thread!
« Reply #54 on: June 24, 2013, 07:43:46 pm »
0
VCAA 2007 exam 2 question 1, the question asks you to sketch five magnetic field lines around the magnet, yet in the assessors report they have 6 lines? wut?

Homer

  • Victorian
  • Forum Obsessive
  • ***
  • Posts: 431
  • Respect: +10
Re: VCE Physics Question Thread!
« Reply #55 on: June 24, 2013, 07:55:32 pm »
0
how would  i find the tension in each cable?
Bachelor of Laws/Engineering

2013 ATAR: 98.65

Specialist Maths [53.06] Maths Methods [48.83] Physics [48.22]

Donuts. Is there anything they can't do?

Phy124

  • Honorary Moderator
  • Part of the furniture
  • *******
  • Posts: 1354
  • Respect: +464
Re: VCE Physics Question Thread!
« Reply #56 on: June 24, 2013, 08:18:47 pm »
0
how would  i find the tension in each cable?
As the structure is in rotational equilibrium you can sum the moments (I think you refer to it as torque in yr 12 physics?) about the point of rotation and equate them to zero.

Hint: The weight force of the bridge and the two vertical components of the tension forces will be the forces that cause rotation. (the horizontal component of tension does not cause rotation as it acts "through" the point of rotation)

Spoiler


2011
Mathematical Methods | Physics | Chemistry | English | Business Management

2012-2017
Bachelor of Science in Applied Mathematics and Bachelor of Civil Engineering (Honours) @ Monash University

Current
Transport Modeller @ Arup

Homer

  • Victorian
  • Forum Obsessive
  • ***
  • Posts: 431
  • Respect: +10
Re: VCE Physics Question Thread!
« Reply #57 on: June 29, 2013, 11:54:24 am »
0
Could someone walk me through this question :)

Thanks

ANS: a) fh=390N, fv=680N
        b) 330N
Bachelor of Laws/Engineering

2013 ATAR: 98.65

Specialist Maths [53.06] Maths Methods [48.83] Physics [48.22]

Donuts. Is there anything they can't do?

SocialRhubarb

  • Victorian
  • Forum Obsessive
  • ***
  • Posts: 313
  • Respect: +34
  • School Grad Year: 2013
Re: VCE Physics Question Thread!
« Reply #58 on: June 29, 2013, 01:08:34 pm »
+1
Part A is quite simple:

The horizontal component is equal to

The vertical component is equal to

Umm, unless I've done something stupid I think your answers are slightly off.

Part B is a bit beyond the scope of VCE.

Essentially what you're doing is equating torques since the object isn't spinning off in one direction.



The net torque on the fence post is 0, so the torque from one source must be equal to the torque from the other.

   Technically there should be a negative somewhere, but whatever.



Alternatively, using the answer of 390N,



Fight me.

Homer

  • Victorian
  • Forum Obsessive
  • ***
  • Posts: 431
  • Respect: +10
Re: VCE Physics Question Thread!
« Reply #59 on: June 29, 2013, 02:14:18 pm »
+1
yeah im not sure why theyve got different component values?
anyways

A 6m ladder of mass 7.5 kg leans against a wall at 60 degrees to the horizontal. What is the torque exerted on the ladder by the weight of the ladder itself?

I know it should be 7.5g x 3 x sin(30), but i dont understand why they take theta as 30 instead of 60?
Bachelor of Laws/Engineering

2013 ATAR: 98.65

Specialist Maths [53.06] Maths Methods [48.83] Physics [48.22]

Donuts. Is there anything they can't do?