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#### Bri MT

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##### Challenging physics questions
« on: January 08, 2019, 03:43:49 pm »
+6
As per the subject, this thread is a place to discuss and solve challenging VCE physics questions.

Don't worry if you have trouble understanding some of these, as I'm posting adaptations of questions that most of the state got wrong in their VCE physics exam. If you have a shot at these questions, I'll post more up - so don't be shy to share what you think the answers might be!

Good luck

(And if I've made any errors feel free to let me know - forgive the slightly dodgy image)
Set 1
1) A ball is bounced against the ground at an angle of 60 degrees to the horizontal and at a speed of 20 metres per second. Ignore air resistance for this question.

a) What horizontal distance does the ball achieve before hitting the ground again?

b) Which graph best represents the kinetic energy of the tennis ball in relation to the horizontal distance from where it contacted the ground?

2) Select the best answer. Under what conditions is the magnetic force on a wire (with current running through it) zero?
a) The wire is parallel to the magnetic field lines
b) The wire is perpendicular to the magnetic field lines
c) The magnetic force is constant regardless of orientation

3) A shopping trolley is pushed at a speed of 2 m/s to the top of a hill and let go. Assume that there is no driving force on the pram and no friction.

a) what speed will it have by the time it reaches the bottom of the 10 m hill?

b) Draw a graph showing the changes in the trolley’s gravitational and kinetic energy as a function of horizontal distance from the top of the hill.
(if you don't know how to attach an image check the guide in the New Users Lounge)
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#### Erutepa

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##### Re: Challenging physics questions
« Reply #1 on: January 08, 2019, 04:40:45 pm »
+4
OK, let's see if we can remember what happened in year 11 physics this year.

1) A ball is bounced against the ground at an angle of 60 degrees to the horizontal and at a speed of 20 metres per second. Ignore air resistance for this question.
a) What horizontal distance does the ball achieve before hitting the ground again?

Break velocity into vertical and horizontal components:
vertical component = 17.32m/s
horizontal component = 10m/s

Find time between ball bounces:
t=[17.32/9.8]*2
t=3.53s

in 3.53 seconds, find horizontal distance covered by ball:
distance (horizontal) = 3.53s*10m/s
distance (horizontal) = 35.34m

b) Which graph best represents the kinetic energy of the tennis ball in relation to the horizontal distance from where it contacted the ground?

B
2) Select the best answer. Under what conditions is the magnetic force on a wire (with current running through it) zero?
a) The wire is parallel to the magnetic field lines
b) The wire is perpendicular to the magnetic field lines
c) The magnetic force is constant regardless of orientation

Now this one is a complete guess (I could google it but that would be cheating  )
C

3) A shopping trolley is pushed at a speed of 2 m/s to the top of a hill and let go. Assume that there is no driving force on the pram and no friction.

a) what speed will it have by the time it reaches the bottom of the 10 m hill?
Eg (top of hill) + Ek (top of hill) = Ek (bottom of hill)
9.8*10 + (1/2) 2^2 = (1/2) (v^2)
98 + 2 =1/2 (v^2)
v=14.14m/s

b) Draw a graph showing the changes in the trolley’s gravitational and kinetic energy as a function of horizontal distance from the top of the hill.
(if you don't know how to attach an image check the guide in the New Users Lounge)
Doiing this in a bumpy car, so you may have to wait for a graph (unless you like spaghetti)

EDIT: after seeing yertles answers, I realised I made a silly mistake in Question 3a which I fixed. I also realised my guess to question 3 is wrong, but it was but a guess and won't change it.
« Last Edit: January 08, 2019, 05:03:29 pm by Erutepa »
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#### Yertle the Turtle

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##### Re: Challenging physics questions
« Reply #2 on: January 08, 2019, 04:46:19 pm »
+4
1.a) 35.3m
b) B

2. A

3.a) 14.14m s-1
sorry can't upload images atm

Explanations:
1. a) Find the horizontal and vertical components, use the 5 formulas of motion to calculate the length of time it takes for the ball to reach maximum height, double it and then multiply by the horizontal component to find distance travelled.
b) There is an acceleration in the vertical axis, so the graph will be non-linear, with a point at which there is still motion in the horizontal axis, so it will not touch the axis.

2. The wire will only experience a force on it when the current is flowing perpendicular to the magnetic field.

3. Equate the total energy at a height of 10m with the total kinetic energy after this has been lost, i.e. 2*m+m*9.8*10=(m*v^2)/2 Therefore 200*m=m*v^2 Hence find v

EDIT: Beaten by Erutepa...
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#### PhoenixxFire

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##### Re: Challenging physics questions
« Reply #3 on: January 08, 2019, 11:15:32 pm »
+3
EDIT: Beaten by Erutepa...
Totally fine for multiple people to have a go at them!
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#### Bri MT

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##### Re: Challenging physics questions
« Reply #4 on: January 12, 2019, 09:44:11 am »
+2
You finished that quicker than I expected, here's another set :
Set 2
A 2.0 kg block (block A) moves to the left at a speed of 8 m/s. It collides with a stationary 4.0 kg block (block b) and rebounds to the right at a speed of 2.0 m/s. What is the speed of block b after the collision?

This one’s more suited to the current year 11 study design (taken from old study design)
VCAA q 8a 2015
“You are provided with four resistors, each of 2.0 Ω. Show how to connect them to produce an effective resistance of 3.0 Ω, using four or fewer resistors. Draw in the space below, so that points A and B are at either end of the effective resistance. Use this symbol for a resistor:  Label the resistors in your diagram R1, R2, R3 and R4. If you used fewer resistors, use fewer labels”

In 8b you then calculate the voltage drop across each resistor.

Again, this isn’t really year 12 knowledge but you do need to use Ohm’s law in year 12 so I thought I’d chuck it in anyway.

For the 3rd question, I’m directing you straight to question 13 of core studies in the VCAA 2015 exam. This one’s pretty diagram heavy so here’s the link to the exam

« Last Edit: January 12, 2019, 11:01:22 am by miniturtle »
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#### Erutepa

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##### Re: Challenging physics questions
« Reply #5 on: January 12, 2019, 10:19:12 am »
+1
You finished that quicker than I expected, here's another set :
Set 2
A 2.0 kg block (block A) moves to the left at a speed of 8 m/s. It collides with a stationary 4.0 kg block (block b) and rebounds to the right at a speed of 2.0 m/s. What is the speed of block b after the collision?

This one’s more suited to the current year 11 study design (taken from old study design)
VCAA q 8a 2015
“You are provided with four resistors, each of 2.0 Ω. Show how to connect them to produce an effective resistance of 3.0 Ω, using four or fewer resistors. Draw in the space below, so that points A and B are at either end of the effective resistance. Use this symbol for a resistor:  Label the resistors in your diagram R1, R2, R3 and R4. If you used fewer resistors, use fewer labels”

In 8b you then calculate the voltage drop across each resistor.

For the 3rd question, I’m directing you straight to question 11 of core studies in the VCAA 2015 exam. This one’s pretty diagram heavy so here’s the link to the exam
question 1
apply conservation of momentum:
let speed of block B = x
2*8 = 4x + 2*-2
16 = 4x -4
4x = 20
x = 5m/s

question 2
Part A:
|----R2----|
A-------R1--|               |-----------B
|----R3----|

Part B:
You didn't give the voltage in the question, but I looked it up and it was 9 volts.
Resistance over R1 = 2 Ohms
effective resistance over R2-R3 = 1 ohm
voltage drop is distributed in a  2:1 ratio
Therefore,
R1=6V
R2=3V
R2=3V

question 3
yeah no yeah.
even with your help below I am a bit lost with the whole magic of magnets. I haven't learned anything about them yet, so I will have to give it a pass.
Thanks for the help though.

bOnUs QueStIoN cause minitutrle tricked me  :'(
Part a:
Had to google the formula for calculating voltage gain:
Av=[V(output)]/[V(input)]
Av=5/0.1
Av=50

Part b:
still not quite sure about this and I know this isn't the entire 3 marks.
The graph shows a non-sinusoidal wave which possess flatened peaks and magnitudes of 8V. This may be due to the speaker possessing a maximum voltage output of 8V.

Part C:
This one was easy enough - I think I was just being a baby about it.
here is the graph

« Last Edit: January 12, 2019, 11:18:11 am by Erutepa »
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#### Bri MT

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##### Re: Challenging physics questions
« Reply #6 on: January 12, 2019, 10:31:36 am »
+1

question 3
no hope of me answering this question, sorry
I haven't covered any of that yet unfortunately

help w/ q3

for flux, draw the change in magnetic field (passing through the coil) over time

emf is related to the rate of change of flux (pretend the flux graph is f(x) and draw f'(x) )
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#### Erutepa

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##### Re: Challenging physics questions
« Reply #7 on: January 12, 2019, 10:53:12 am »
0
help w/ q3

for flux, draw the change in magnetic field (passing through the coil) over time

emf is related to the rate of change of flux (pretend the flux graph is f(x) and draw f'(x) )
This feedback does not seem to be for question 11 of the 2015 physics paper.
Question 11 seems to be talking about voltage inputs and outputs of an amplifier.
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#### Bri MT

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##### Re: Challenging physics questions
« Reply #8 on: January 12, 2019, 11:01:48 am »
+1
This feedback does not seem to be for question 11 of the 2015 physics paper.
Question 11 seems to be talking about voltage inputs and outputs of an amplifier.

Sorry! that was supposed to say q 13
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#### Erutepa

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##### Re: Challenging physics questions
« Reply #9 on: January 12, 2019, 11:08:05 am »
+1
Sorry! that was supposed to say q 13
I just updated my post with question 11, but I shall now try question 13
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