ATAR Notes: Forum

National Education => General National Education Discussion => Interstate Discussion and Comparison => Topic started by: Bri MT on January 08, 2019, 03:43:49 pm

Title: Challenging physics questions
Post by: Bri MT on January 08, 2019, 03:43:49 pm
As per the subject, this thread is a place to discuss and solve challenging 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!

Please note that this thread isn't just for VCE students: HSC & QCE students are also very welcome to use it for their practice

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?
(https://i.imgur.com/WPMZ3uh.png)

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)
Title: Re: Challenging physics questions
Post by: Erutepa on January 08, 2019, 04:40:45 pm
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.
answer
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?
(https://i.imgur.com/WPMZ3uh.png)
answer
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  ;) )
answer
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?
answer
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. :)
Title: Re: Challenging physics questions
Post by: Yertle the Turtle on January 08, 2019, 04:46:19 pm
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... :'(
Title: Re: Challenging physics questions
Post by: PhoenixxFire on January 08, 2019, 11:15:32 pm
EDIT: Beaten by Erutepa... :'(
Totally fine for multiple people to have a go at them!
Title: Re: Challenging physics questions
Post by: Bri MT on January 12, 2019, 09:44:11 am
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

Title: Re: Challenging physics questions
Post by: Erutepa on January 12, 2019, 10:19:12 am
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
(https://imgur.com/a/PhNelhU.jpeg)
Title: Re: Challenging physics questions
Post by: Bri MT on January 12, 2019, 10:31:36 am

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) )
Title: Re: Challenging physics questions
Post by: Erutepa on January 12, 2019, 10:53:12 am
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.
Title: Re: Challenging physics questions
Post by: Bri MT on January 12, 2019, 11:01:48 am
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
Title: Re: Challenging physics questions
Post by: Erutepa on January 12, 2019, 11:08:05 am
Sorry! that was supposed to say q 13
I just updated my post with question 11, but I shall now try question 13 :)
Title: Re: Challenging physics questions
Post by: Erutepa on January 20, 2020, 10:33:18 am
The science games have begun

As such, it is time for a freshly baked batch of challenging questions!
If you want to score points for the science games, you can do so by answering questions in (and after) this post here. Feel free to answer the questions before this, however you won’t earn science games points (but you will still get fantastic revision/learning out of it)
These challenging questions are past VCAA exam questions on which 50% of the state didn’t get full marks (for multiple choice questions) or for which the average mark is less than half of the full available marks (for short answer questions). Please note that while these questions are from VCE study designs, since there is significant overlap between science across the different states, most of these questions should be able to be answered by those from other states.
This thread will be updated weekly with a new batch of 5 Multiple Choice questions and 10 Marks worth of Short Answer questions.
Here is your first batch:

Multiple Choice
Question 1
The transformer delivers 48 WRMS to a resistor. Assume that the transformer is ideal. Which one of the following best gives the peak current in the secondary coil?
A.   0.2 A
B.   4.0 A
C.   5.7 A
D.   11.3 A
Question 2
At one point on Earth’s surface at a distance R from the centre of Earth, the gravitational field strength is measured as 9.76 N/kg.
Which one of the following is closest to Earth’s gravitational field strength at a distance 2R above the surface of Earth at that point?
A.   1.08 N/kg
B.   2.44 N/kg
C.   3.25 N/kg
D.   4.88 N/kg
 
Question 3
Anna and Barry have identical quartz clocks that use the precise period of vibration of quartz crystals to determine time. Barry and his clock are on Earth. Anna accompanies her clock on a rocket travelling at constant high velocity, v, past Earth and towards a space lab (which is stationary relative to Earth), as shown in Figure 1.
(https://imgur.com/F3WZ3BN.jpeg)

Which one of the following statements correctly describes the behaviour of these two clocks?
A.   The period of vibration in Anna’s clock (as observed by Anna) will be shorter than the period of vibration in Barry’s clock (as observed by Barry).
B.   The period of vibration in Anna’s clock (as observed by Anna) will be longer than the period of vibration in Barry’s clock (as observed by Barry).
C.   The period of vibration in Anna’s clock (as observed by Anna) will be the same as the period of vibration in Barry’s clock (as observed by Barry).
D.   Only the time on Barry’s clock is reliable because it is in a frame that is not moving
 
Question 4
Yasmin and Paul set up the following experiment in a large open area. They connect two speakers that are facing each other, as shown in Figure 2. Both speakers are connected 10 m apart to the same signal generator and amplifier, which is producing a sound with a wavelength of 1.0 m.
 (https://imgur.com/L2VlUFv.jpeg)

Yasmin stands in the centre, equidistant to speakers A and B. She then moves towards Speaker B and experiences a sequence of loud and quiet regions. She stops at the second region of quietness.
How far is she from Speaker B?
A.   0.75 m
B.   1.25 m
C.   2.75 m
D.   4.25 m
 
question 5
A person moving parallel to the length of a 2.00 m ruler observes the change of length of this ruler due to relativity to be 0.010 m.
What is the person’s speed relative to the ruler?
A.   0.0050c
B.   0.010c
C.   0.10c
D.   0.90c
Short Answer
Question 1
Charon, a moon of Pluto, has a circular orbit
(https://imgur.com/m9LmarK.jpeg)

a) Calculate the period of orbit of Charon. Show your working. (3 marks)

b) Scientists wish to place a spacecraft, of mass 1000 kg, in an orbit of the same radius as Charon. Three students, Rick, Melissa and Nam, are discussing the situation and have different opinions.    
Rick says as the spacecraft is lighter, it will have to move at a greater speed than Charon to achieve the same orbit.    
Melissa says the spacecraft would need to move at the same speed as Charon.    
Nam says the spacecraft would need only to move at a lower speed as it is lighter than Charon.    
Evaluate these three opinions. Detailed calculations are not necessary. (3 marks)

Question 2
Figure 5 shows a generator at an electrical power station that generates 100 MWRMS of power at 10 kVRMS AC.
Transformer T1 steps the voltage up to 500 kVRMS AC for transmission through transmission wires that have a total resistance, RT, of 3.0 Ω. Transformer T2 steps the voltage down to 50 kVRMS AC at the substation. Assume that both transformers are ideal.
(https://imgur.com/VfY0ND3.jpeg)

Transformer T1 stepped the voltage up to 250 kVRMS AC instead of 500 kVRMS AC.    
By what factor would the power loss in the transmission lines increase? (2 marks)
Question 3
A roller-coaster is arranged so that the normal reaction force on a rider in a car at the top of the circular arc at point P, shown in Figure 7, is briefly zero. The section of track at point P has a radius of 6.4 m.
(https://imgur.com/qdivyPz.jpeg)
Calculate the speed that the car needs to have to achieve a zero normal reaction force on the rider at point P (2 marks)
 

When Answering your questions, please write your answer inside of a spoiler like this:
question 1
Spoiler
This is my answer
The reason behind this is just so that other users who are having a go at answering these questions don’t accidentally see what others have put down and can have a go at it themselves.
I would also like to encourage everyone to have a go at answering these questions without looking at other user’s responses – this will help develop your ability to really critically think about a question independently. Remember, there is no harm in getting something wrong and making a mistake is an opportunity to learn!
Title: Re: Challenging physics questions
Post by: Erutepa on February 03, 2020, 09:21:30 pm
As we are entering the second half of the epically epic science games, its as good a time as ever to jump into this thread and answering some tough questions.
Since last weeks questions didn't see to much activity, there won't be a fresh batch of questions this week as I don't want to bombard users with too many questions. So for now, the first group of questions will sit here patiently waiting to be answered.
If you haven't had a go yet at any questions or have only answered some of the questions, now would be a great time to have a crack at them and earn some points. And remember, don't worry about being wrong - if you make an error or get the wrong answer, we can give you some feedback and hopefully guide you to the correct answer!
Title: Re: Challenging physics questions
Post by: DrDusk on February 03, 2020, 10:50:02 pm
As we are entering the second half of the epically epic science games, its as good a time as ever to jump into this thread and answering some tough questions.
Since last weeks questions didn't see to much activity, there won't be a fresh batch of questions this week as I don't want to bombard users with too many questions. So for now, the first group of questions will sit here patiently waiting to be answered.
If you haven't had a go yet at any questions or have only answered some of the questions, now would be a great time to have a crack at them and earn some points. And remember, don't worry about being wrong - if you make an error or get the wrong answer, we can give you some feedback and hopefully guide you to the correct answer!
I'm probably not allowed to participate.. I feel it would just be cheating at that point.
I will contribute some juicy questions though!
Title: Re: Challenging physics questions
Post by: Bri MT on February 05, 2020, 09:56:48 am
I'm probably not allowed to participate.. I feel it would just be cheating at that point.
I will contribute some juicy questions though!

You can participate if you'd like (only restriction is that mods can't) but I understand if you'd feel more comfortable participating in different ways (examples of other options for physics: physics misunderstandings, making practice questions, contributing to a question chain, making a guide on a topic)