VCE Physics Question Thread!

[TooLazy]

Where?
"Einstein’s theory of special relativity
•    describe Einstein’s two postulates for his theory of special relativity that:
–    the laws of physics are the same in all inertial (non-accelerated) frames of reference
–    the speed of light has a constant value for all observers regardless of their motion or the motion of the source
•    compare Einstein’s theory of special relativity with the principles of classical physics
•    describe proper time (t0 ) as the time interval between two events in a reference frame where the two events
occur at the same point in space
•    describe proper length (L0 ) as the length that is measured in the frame of reference in which objects are at rest
•    model mathematically time dilation and length contraction at speeds approaching c using the equations:
•    explain why muons can reach Earth even though their half-lives would suggest that they should decay in the
outer atmosphere."

I can't find it in the study design?
The Edrolo person also said it isn't on the course this year as well

My teacher said it was so not 100% sure.
Also Ive watched edrolo videos on it...? Like the guy solves questions involving relativistic mass etc

[Bri MT]

My teacher said it was so not 100% sure.
Also Ive watched edrolo videos on it...? Like the guy solves questions involving relativistic mass etc

I think that might be because it helps for understanding the Ek equation & because it was assessed in the past.
Might be one of things where it's the two different Edrolo people?
Mass dilation isn't on the formula sheet whereas length contraction and time dilation. It is, however, a bit strange to exclude mass (only) given how similar the calc is to time....

[TooLazy]

I think that might be because it helps for understanding the Ek equation & because it was assessed in the past.
Might be one of things where it's the two different Edrolo people?
Mass dilation isn't on the formula sheet whereas length contraction and time dilation. It is, however, a bit strange to exclude mass (only) given how similar the calc is to time....

Apparently the bio exam had stuff that wasnt explicitly stated on the study design.
Since both physics and bio are new designs this year, I definitely wouldnt take any risks.

and yeah also, vcaa are pretty dog so...

[chantelle.salisbury]

Hey..
just wondering if someone could help me with uncertainty percentages and absolute errors? firstly how do i calculate these?
this is a sample q.
An atomizer sprays a fine mist of spherical oil droplets. the radius of one of the droplets is 1.37(plus minus) .02 micro m
calculate the volume (including uncertainty) V of the oil droplet, given V=4/3pie.r^2

[Bri MT]

Hey..
just wondering if someone could help me with uncertainty percentages and absolute errors? firstly how do i calculate these?
this is a sample q.
An atomizer sprays a fine mist of spherical oil droplets. the radius of one of the droplets is 1.37(plus minus) .02 micro m
calculate the volume (including uncertainty) V of the oil droplet, given V=4/3pie.r^2

The absolute uncertainty is 0.02 *10^-6m.
The percentage uncertainty is (0.02/1.37)*100
Your percentage uncertainty on the sphere would be 2*((0.02/1.37)*100)   (it is times 2 because r is squared)

More info:https://atarnotes.com/forum/index.php?topic=174013.0

[-273.15]

Hello has anyone done question 14b from the sample exam?
in terms of the uncertainty value, both itute and vicphysics solutions had different values
I also found a different value
Im not sure how to find the uncertanty correctly? What values have others calculated
Also do you think vcaa would be a bit lenient with uncertainty values?

[manishmao]

Any help with this question?
Jason and Kylie are sitting at the northern and southern ends respectively of a train carriage travelling north at
a high speed. Each holds a torch that they turn on and off. Harold is standing on a platform beside the train. As
the midpoint of the carriage passes Harold, he observes simultaneous light flashes from both Jason and Kylie.
Which one of the following statements is true?
A. To an observer inside the carriage, located at its midpoint, Jason and Kylie turned on their torches at the
same time.
B. To an observer inside the carriage, located at its midpoint, Jason turned on his torch before Kylie.
C. To an observer inside the carriage, located at the midpoint, Kylie turned on her torch before Jason.
D. It does not make any sense to ask in which order Jason and Kylie turned on their torches, because Einstein
showed that time is relative.

Answer is C

[KiNSKi01]

Any help with this question?
Jason and Kylie are sitting at the northern and southern ends respectively of a train carriage travelling north at
a high speed. Each holds a torch that they turn on and off. Harold is standing on a platform beside the train. As
the midpoint of the carriage passes Harold, he observes simultaneous light flashes from both Jason and Kylie.
Which one of the following statements is true?
A. To an observer inside the carriage, located at its midpoint, Jason and Kylie turned on their torches at the
same time.
B. To an observer inside the carriage, located at its midpoint, Jason turned on his torch before Kylie.
C. To an observer inside the carriage, located at the midpoint, Kylie turned on her torch before Jason.
D. It does not make any sense to ask in which order Jason and Kylie turned on their torches, because Einstein
showed that time is relative.

Answer is C

Yo manishmao!

<reference to other forum removed>

-"The train is travelling north, and Kylie is at the south. The torch is turned on when the MIDPOINT of the train reaches Harold. At this point, Jason is now travelling AWAY from Harold, whereas Kylie is still travelling towards.

When the light ray comes out of their torches, it will bend towards the northerly direction (c is constant in all frames of references). If Jason's light ray is bent north, it's only getting further away from Harold. Whereas if KYLIE's light ray is bent north, it's actually doing the opposite and getting closer."

<reference to other forum removed>

Moderator action - insanipi: Removed references to rival forums.

[Nicko912]

Just asking to be sure, but with physics are the answers accepted when their reasonable? I know with chemistry you have to simplify to the correct number of sigfigs, I've been doing sigfigs for physics too just for memory sake, do they accept this too?

[TooLazy]

Just asking to be sure, but with physics are the answers accepted when their reasonable? I know with chemistry you have to simplify to the correct number of sigfigs, I've been doing sigfigs for physics too just for memory sake, do they accept this too?

Yeah I think there is just one question, where they test you on sig figs. Other than that i think if your answers are reasonable you shouldnt have an issue

[sweetiepi]

Just asking to be sure, but with physics are the answers accepted when their reasonable? I know with chemistry you have to simplify to the correct number of sigfigs, I've been doing sigfigs for physics too just for memory sake, do they accept this too?

Last year I believe it was perfectly fine to just be sensible with sigfigs, however best practice is to always be careful with sigfigs

[Nicko912]

Yeah I think there is just one question, where they test you on sig figs. Other than that i think if your answers are reasonable you shouldnt have an issue

Thanks for the responses!

Yeah mainly to what I was getting at, if it's safer to use sigfigs or to just use reasonable answers, the difference between a sigfig answer and a calculator answer can be quite different at times. I've seen in VicPhysics solutions they consistently use sigfigs, but they're not VCAA, so I guess it doesn't matter at all that much.

[yewyewyewy]

General questions about voltage;
Why can you have negative voltage (AC) ? Doesn't that imply we can have "negative" energy? Wouldn't it be best if we have negative and positive current for saying which way the current flow?
Also;
I lost a mark on a SAC with the question being about explainging how seatbelt and crumpling reduce the severity of the drivers injury, it was a 3 mark question. What type of exam "style" answers should I have. The teacher noted on it "how does the seat belt increase the time of collision?", how would I undergo answering that for an 'exam' quality answer?
Thanks

The negative symbol implies direction not magnitude so whilst 2V=-2V in terms of magnitude the understanding is that the latter flows in the opposite direction. 3 marks indicates that the examiner is looking for 3 distinct points, look to include relevant physics principles supported by formulas, so perhaps you could say:

• F=ma=mv/t
• Therefore impact force is inverse proportional to change in time
• Seatbelts and crumpling increase the collision time therefore decreasing the force of the collision

[simrat99]

Hi, just to confirm, we are not required to know about the Michelson Morley experiment, right?

[kalopsia]

Hi, just to confirm, we are not required to know about the Michelson Morley experiment, right?

No, I don't think so. The study design states that we have to 'compare Einstein’s theory of special relativity with the principles of classical physics', so it would probably help if you know about it though.