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October 22, 2019, 09:33:04 am

Author Topic: Syndicate's Physics Exam tips (Unit 3) 2017  (Read 2545 times)  Share 

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Syndicate

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Syndicate's Physics Exam tips (Unit 3) 2017
« on: November 22, 2017, 05:57:33 pm »
+29
Hi Guys,
I am no 50er, and doubt I'll get close to a 50 anyways (I am also yet to receive my marks this year). I've decided to write down all my notes, and a few tips for future physics students, hoping that it helps them with the current study design. Right now, I am only posting my Unit 3 Notes, and if (hopefully) I get the time, I'll post ones for Unit 4   :)


Unit 3 Content
Motion (from Units 1/2)
Circular Motion
Projectile Motion
Relativity
Fields
Electric Power Generation

I found that it was too long, so I broke it up into different parts using spoilers  :)
General: 
Spoiler
-   Read the question twice! I know its time-consuming but if you move efficiently it will decrease the probability of you losing marks on stupid mistakes (Using a highlighter would be great as well)

-   Make sure you clearly look at the units labelled on the axis (really helpful in many cases)
-   Try to do at least 5-6 MC questions in the reading time, as it would allow you to get a bit of head start.

-   Start exam revision by mid-September at most (and do at least 10-12 exam under timed condition). I started it a bit late, and had to sacrifice my sleep over it  :P

-   In regards to worded question, I think you should start by looking at the number of marks associated with that question. If there are 2 marks, make 2 statements (unless there is a bit of calculation involved), and likewise if it is 3 marks, then make 3 statements. For questions involving mainly calculations, make sure you have a neat working out (step-by-step, and write down the formulas you are using to obtain your solution- it might get you some marks just in case you get your answer wrong)

-    USE THE STUDY DESIGN! - this one is extremely important not only for physics but all your subjects (especially the science ones)
Motion (prerequisites):
Spoiler
1.   Understand the concepts really well, especially with all the springs stuff (there has been a question on springs nearly every year!)
-   With springs, I think it best to understand in what cases you can use energy conversions to calculate the spring constant (ie. When the spring is reciprocating)- VCAA Physics 2010 Question 13, and when to equate the weight force to Hookeís law (ie. When the spring is at rest)- VCAA Physics 2016 Question 3. There also have been questions asking you to draw the total energy (remains constant), spring potential energy (either increase or decrease quadratically), gravitational potential energy (increases or decreases at the linear rate), and kinetic energy (maximum in the middle, and is at 0J at the start and end).

2.   Make sure that you know how to do momentum/ impulse questions really well (they are really common)

3.   Write down all the derived formulas for banked tracks on your reference sheet.
-   Note that if they ask you to draw the FORCES ACTING ON THE BODY, make sure you only down the normal force, weight force and friction (if it applies). Also, that friction will be acting towards the centre, and at the bottom of the body along the banked track.
-   Note that the formula to find the angle only works if there is a smooth surface (no friction)

4.   With drawing forces, the weight force must be drawn from the centre of the body, the normal force from the bottom, and the frictional force along the surface.
Force Body Diagram

5.   You should ensure that you know how to calculate acceleration/force/ work etc... from either calculating the gradient of the tangent, or the area beneath the graph line.
Area/Slope calculations
Projectile motion:
Spoiler
There is usually one question on projectile motion every year, so make sure you know all the key concepts (ie. Vertical velocity is 0 m/s on top of its motion, horizontal velocity is constant if there is no air resistance, air resistance decreases the range etcÖ). I found that there are three types of questions that can come up on the exam.
1.   A projectile which has a zero-vertical displacement (so a projectile that begins and finishes on the ground).
-   For these sort of questions, do note that the final velocity will always be equal to the initial velocity (given that there is no air resistance acting on the projectile). ie. VCAA Physics 2016 Question 5, VCAA Physics 2014 Question 3a
Spoiler
2.   A projectile which has some sort of vertical displacement, and are launched at the (ie. A projectile is launched from a top of the cliff, and hits the ground).
-   Students find these sorts of questions quite hard, so itís best to do as many of this type as you can. ie. VCAA Physics 2015 Question 5, VCAA Physics 2014 Question 3b
Spoiler
Tip: When you are try to find the final velocity, donít break the motion of projectile into two different parts (ie. From beginning to top, and top to final), but instead consider it as a whole and assign positive/ negative directions as either up/down)

3.   (This one is really uncommon) A projectile which has some sort of vertical displacement, and are launched parallel to the horizontal. I couldnít really find an example on this, but itís best to know how to do it (No one knows what can come up next year!)
Spoiler
Circular Motion:
Spoiler
Again, like projectile motion, I found that there were three types of questions that were quite common in exams.
1.   Vertical circular motion
-   Make sure to consider all the forces acting on the system (especially their magnitude). So, if the question asks you to draw and label all the forces acting a pendulum at the bottom of itís swing, youíll need to draw the tension with a greater magnitude than the weight force) ie VCAA Physics 2015 Question 3
Spoiler

2.   Horizontal circular motion
-   Havenít seen this one for a while with VCAA, but there are quite on company exams that you may come across. Some applications from these are usually involving some sort of a pendulum moving in a horizontal circle.
 
3.   Energy conversions/ force questions- basically these questions ask you to calculate the speed of the body at the certain position in its motion.
-   Itís best to write down the derived formulas for this on your reference sheet, and do as many of these as you can (ie. VCAA Physics 2014 Question 4
Relativity:
Spoiler
1.   Note that proper time is the time measured in the same frame, and proper length is the
length measured in the rest frame.
-   ie. A scientist measures the half-life of a muon to be A seconds, and the length of the mountain to be B km. Now the proper time in this case is NOT A seconds, as that is not measured in the frame of the muons, whilst the proper length is B km, as the mountain and scientist are at rest relative to each other. Hence, the scientist observes a greater half-life for muons, whilst the muons observe a shorter length of the mountain.

2.   You should be able to compare Einsteinís two postulates with Newtonian mechanics, and be able to show how Newtonian/ Galilean relativity cannot apply to objects with a really small mass with huge velocities.

3.   Note that speed of light can VARY, as it depends on the electrical and magnetic properties of the medium. Specifically, the strength of the electric force between stationary charges and the strength of the magnetic force between charges.

4.   Understand why/ how sun is losing its mass over time (they might ask you to find out how much mass is being lost, which is basically E = mc^2 to E = power x time).
Fields:
Spoiler
1.   To indicate that the field is stronger at the certain place, draw the field lines closer.
-   Note that for uniform electric fields, draw the field lines equally spaced, as the field strength is constant between the two plates.
Field Strength
2.   Gravitational field/force questions.
-   These ones usually involve finding the force between two objects (note: Newtonís third law indicates that the gravitational force acting on both objects will be the same), and the acceleration/ gravitational field strength on the surface of some planet (make sure you now all the units! There was a question like this on the exam this year). Furthermore, you can also be asked to find the radius or period of some object in orbit, and its best to use Keplerís law for this (put it on your reference sheet).
-   Make sure you also know all the properties of a geostationary satellite (ie. periodL24 hours, orbits over the equator of the planet etc.) VCAA Physics 2016 Question 6
-   Understand the difference between apparent weight (W = N), weight, apparent weightlessness (Normal force = 0 N) and weightlessness (g = 0 Nkg^-1) ie. VCAA Physics 2013 Question 7c. You can also be asked to calculate the apparent weight of some object ie. VCAA Physics 2009 Exam 1 Question 7
-   Make sure you also know how to calculate the work down from a gravitational field strength vs. distance graph, and gravitational field strength per kilogram vs. distance graph.

3.   Electrical fields- Students usually find this one easier than gravitational fields
-   So, it basically involves calculating the electric field strength between two plates that form uniform electric fields (using E = V/d).

4.   Magnetic fields
-   Understand how to use the right-hand rule, the right-hand slap rule and the right-hand slap rule for solenoids! (Note that the thumb only points in the direction of conventional current, so if the electron is moving towards the right, your thumb would point towards the left).
-   Make sure that you know how to calculate force on moving particles, and current carrying wires using F = qvB and F = NILB respectively.
-   The consequences of changing mass, velocity, magnetic field strength or charge on the radius of a moving charge moving through a magnetic field perpendicular to its motion (r= mv/qB).
-   Regarding the DC Motor, you should also know that it converts electrical energy to mechanical energy and how a split ring commutator works (it reverses the current every half turn when the coil is at a right angle to the magnetic field). To increase the force/ torque, you can either have more loops, increase the current, have a stronger magnetic field or increase the battery voltage). There are lots of questions on DC Motor out there, so it shouldnít be that hard to find one on this (Also note that you donít have to know about AC motors at all from this year).
Electric Power:
Spoiler
1.   Electricity is only generated when there is a change in magnetic flux (flux = BA- note there is no N (the number of loops)).
-   With this, youíll have to know Lenz Law, and calculate the direction of induced current through the right-hand rule for solenoids (the direction of induced magnetic fields is such that it is opposite to the direction of the change in magnetic field).

-   The graph of EMF generated is the negative of the derivative of the graph of the change in flux (as per Shadow's correction- E = -d(BA)/dt)
Spoiler
2.   Make sure you know that difference between an Alternator and a DC generator (and the merits of using an Alternator over DC generator- which is basically that transformers donít work with DC current, as there is no change in magnetic flux)
-   You should know the differences between slip-ring and split-ring commutators, and their graphs of EMF generated
EMF generated
-   How can you generate greater EMF? (more loops, greater magnetic strength increase frequency)

Feel free to ask any questions here or PM me if you want  :)
« Last Edit: November 23, 2017, 12:22:53 am by Syndicate »
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Physics Guide 2017

Bri MT

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Re: Syndicate's Physics Exam tips (Unit 3) 2017
« Reply #1 on: November 22, 2017, 09:40:05 pm »
+3
I think some people might read "   The graph of EMF generated is the derivative of the graph of the change in flux." as EMF being the derivative of the rate of change of flux, but that's the only concern point I found.

Definitely agree with your point about reading graphing units carefully, I once calculated that 32000 kJ of energy was needed to take a rocket into orbit from Earth's surface....


Thanks for the great post, I'm sure a lot of people will find it very useful :)
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Syndicate

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Re: Syndicate's Physics Exam tips (Unit 3) 2017
« Reply #2 on: November 22, 2017, 10:47:53 pm »
+3
I think some people might read "   The graph of EMF generated is the derivative of the graph of the change in flux." as EMF being the derivative of the rate of change of flux, but that's the only concern point I found.

Haha thanks for noticing the mistake! This concept is definitely important :D
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Shadowxo

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Re: Syndicate's Physics Exam tips (Unit 3) 2017
« Reply #3 on: November 22, 2017, 11:13:06 pm »
+3
Haha thanks for noticing the mistake! This concept is definitely important :D
And also it's the negative of the derivative (E = -d(BA)/dt)
It might be clearer to say "... is the negative of the derivative of the flux graph"

PS great guide :D
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Syndicate

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Re: Syndicate's Physics Exam tips (Unit 3) 2017
« Reply #4 on: November 23, 2017, 12:05:52 am »
+1
And also it's the negative of the derivative (E = -d(BA)/dt)
It might be clearer to say "... is the negative of the derivative of the flux graph"

PS great guide :D

Haha yea you are right (so many careless mistakes! :P). I'd better change it before there's any confusion! :D
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Syndicate

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Re: Syndicate's Physics Exam tips (Unit 3) 2017
« Reply #5 on: March 21, 2018, 07:32:31 pm »
+4
bump

Just wanting to let the current physics students look at this quick summary of Unit 3 Physics.
2017: Chemistry | Physics | English | Specialist Mathematics | Mathematics Methods
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Physics Guide 2017