HSC Physics Question Thread

[blyatman]

Can someone please help with this q?

"When the Apollo astronauts switched off their rocket engine their initial kinetic energy carried them to the Moon. How did the apparent weight of the astronauts change as they travelled to the Moon?

(A) Their apparent weight remained zero until they switched on the rocket engines near the Moon.
(B) Their apparent weight decreased as they moved further from the Earth and then increased as they approached the Moon
(C) Their apparent weight increased as they moved further from the Earth and then decreased as they approached the Moon
(D) Their apparent weight decreased throughout the flight."

I'm a bit confused with the concept of apparent weight altogether.

Any help is greatly appreciated

If you read the short wiki article on apparent weight, you should be able to answer this q.

The apparent weight is equal to the normal reaction force, and is more or less the force that one would "feel".

[DrDusk]

If you read the short wiki article on apparent weight, you should be able to answer this q.

The apparent weight is equal to the normal reaction force, and is more or less the force that one would "feel".

This.
Apparent weight as the name suggests is the weight you 'feel'. The reason you feel your weight on the Earth is because relative to you the Earth is stationary and you are being accelerated downward by gravity onto the surface of the Earth.

However if you are in a rocket ship when no engines are being fired, the floor of the rocket will have an acceleration downward and so will you! So relative to the rocket ship you have zero acceleration, leading to you not feeling your weight, as compared to on Earth where your being accelerated against the floor your standing on by gravity.

Now try and answer that question.

[not a mystery mark]

Hey, would somebody be able to explain my teachers answer to this question? Majorly confused. Why wouldn't the cathode rays be deflected by an electric field if they're electrons? Thanks!

Note:
Column One is the experiment, Column Two has the Observation, Column Three is the conclusions drawn from each observation.

[DrDusk]

Hey, would somebody be able to explain my teachers answer to this question? Majorly confused. Why wouldn't the cathode rays be deflected by an electric field if they're electrons? Thanks!

Note:
Column One is the experiment, Column Two has the Observation, Column Three is the conclusions drawn from each observation.

Lol of course they would be deflected by an Electric field if they were charged particles.

The thing is Scientists back in the day were really bad at detecting deflections and so they were unable to see that it deflected due to the electric plates. Which led to the conclusion that the Cathode ray is a wave and not a particle for that experiment. This conclusion was later proven to be incorrect and deflections were observed.

[not a mystery mark]

Lol of course they would be deflected by an Electric field if they were charged particles.

The thing is Scientists back in the day were really bad at detecting deflections and so they were unable to see that it deflected due to the electric plates. Which led to the conclusion that the Cathode ray is a wave and not a particle for that experiment. This conclusion was later proven to be incorrect and deflections were observed.

Ah okay cool. This literally had my head hurting all day. Every time I would google it kept saying that JJ Thompson saw deflection. Hertz had to come fool everyone with his errors ahaha.

Thanks heaps, and also cool profile pic 

[DrDusk]

Thanks heaps, and also cool profile pic 

Haha thanks, I'm making them for a Poster/Youtube channel where I can make videos for HSC/Prelim Physics, so I figured why not have it as a pic lol

[Coolmate]

Hi Everyone!

I was just wondering if anyone would happen to have any example questions that I could complete for the Module 4, syllabus topic on Electricity and Magnetism dot point (I have attached the dot point) for practice? Also, if anyone has any good short answer/ extended written response questions that I could practice also? 

Thanks in advance,

Coolmate

[DrDusk]

Hi Everyone!

I was just wondering if anyone would happen to have any example questions that I could complete for the Module 4, syllabus topic on Electricity and Magnetism dot point (I have attached the dot point) for practice? Also, if anyone has any good short answer/ extended written response questions that I could practice also? 

Thanks in advance,

Coolmate

I don't see any attachment?

[Coolmate]

Oh! Sorry...... it's attached to this post 

[DrDusk]

Oh! Sorry...... it's attached to this post 

Have you tried the sample paper posted by Blasonduo. If you scroll down you should find it. IIRC it has questions relating to this...

[Coolmate]

Hey DrDusk,

Thankyou, I just found it and the questions were great and very useful!

Cheers,

Coolmate

[louisaaa01]

Just came across this question and am very confused.

"Which fundamental quantity required that its unit of measurement be redefined following acceptance of the theory of special relativity?

(A) Luminous intensity
(B) Length
(C) Mass
(D) Time "

Any help would be very much appreciated!

[blyatman]

Just came across this question and am very confused.

"Which fundamental quantity required that its unit of measurement be redefined following acceptance of the theory of special relativity?

(A) Luminous intensity
(B) Length
(C) Mass
(D) Time "

Any help would be very much appreciated!

I believe the answer is B, though I don't think any of them are right tbh. Luminosity intensity is clearly not related. The other variables (mass, length, and time) do not change within an inertial frame of reference: a meter is still a meter, a second is still a second, and a kilogram is still a kilogram.

Context: the previous definitions of a meter and kilogram were based off arbitrary objects stored in an arbitrary vacuum chamber in France. Every year, scientific institutes around the world would send their copies of a meter and kilogram to France to calibrate them against the official one in France. Cleaning the objects etc would often cause small layers to shed off, and thus the definition of a kilogram and meter changed every year. As a result, there needed to be a more robust way of defining the meter and the kilogram. I don't know the original definition of a second but you could look that up (it was also probably arbitrary).

1 second was redefined as the period it took for electrons to bounce a certain number of times between energy levels of the Caesium atom.

1 meter was redefined as a fraction of the distance that light travels in one second.

1 kg was only redefined up until very recently in the last year or two from what I recall (I'm not clear on the specifics).

The reason I believe the answer to your question is B is because the redefined unit of length is the only one whose definition directly depends on the speed of light. However, I don't know if it was necessarily REQUIRED its unit of measurement to be redefined. I guess one could argue that the meter ruler will contract according to observers in other inertial frames. However, in your frame it doesn't change and you could always use the meter ruler in your reference frame to measure lengths, so the old definition of the meter would still work in your inertial frame. Scientists just wanted a new definition of a meter that wasn't depended on some arbitrary object stored in a vacuum chamber in France. The constancy of the speed of light provided this solution, as it meant that the meter could now have its definition redefined in terms of universal constants.

[Coolmate]

Hey lousiaaa01!

DISCLAIMER: I am in year 11 so I may not be correct!

Yes, this is a confusing question, but I would guess that it is option "B"?

I chose this option because I think that length can be redefined depending on where you are standing and observing the event from. This is due to the Theory of Special Relativity, being said to have the length of an object moving at relativistic speeds can and will contract along the direction of motion. Whereas an observer not moving and just observing (relative to the moving object) will see the object to be shorter in length.

Therefore, length can be redefined due to the Theory of Special Relativity P.S. I also feel as though this is the only unit which can actually change in regards to the Theory of Special Relativity!

The Physics Classroom Website Below explains further:

https://www.physicsclassroom.com/mmedia/specrel/lc.cfm

I hope this helps and please take my response with a grain of salt

Coolmate

[louisaaa01]

I believe the answer is B, though I don't think any of them are right tbh. Luminosity intensity is clearly not related. The other variables (mass, length, and time) do not change within an inertial frame of reference: a meter is still a meter, a second is still a second, and a kilogram is still a kilogram.

Context: the previous definitions of a meter and kilogram were based off arbitrary objects stored in an arbitrary vacuum chamber in France. Every year, scientific institutes around the world would send their copies of a meter and kilogram to France to calibrate them against the official one in France. Cleaning the objects etc would often cause small layers to shed off, and thus the definition of a kilogram and meter changed every year. As a result, there needed to be a more robust way of defining the meter and the kilogram. I don't know the original definition of a second but you could look that up (it was also probably arbitrary).

1 second was redefined as the period it took for electrons to bounce a certain number of times between energy levels of the Caesium atom.

1 meter was redefined as a fraction of the distance that light travels in one second.

1 kg was only redefined up until very recently in the last year or two from what I recall (I'm not clear on the specifics).

The reason I believe the answer to your question is B is because the redefined unit of length is the only one whose definition directly depends on the speed of light. However, I don't know if it was necessarily REQUIRED its unit of measurement to be redefined. I guess one could argue that the meter ruler will contract according to observers in other inertial frames. However, in your frame it doesn't change and you could always use the meter ruler in your reference frame to measure lengths, so the old definition of the meter would still work in your inertial frame. Scientists just wanted a new definition of a meter that wasn't depended on some arbitrary object stored in a vacuum chamber in France. The constancy of the speed of light provided this solution, as it meant that the meter could now have its definition redefined in terms of universal constants.

Hey lousiaaa01!

DISCLAIMER: I am in year 11 so I may not be correct!

Yes, this is a confusing question, but I would guess that it is option "B"?

I chose this option because I think that length can be redefined depending on where you are standing and observing the event from. This is due to the Theory of Special Relativity, being said to have the length of an object moving at relativistic speeds can and will contract along the direction of motion. Whereas an observer not moving and just observing (relative to the moving object) will see the object to be shorter in length.

Therefore, length can be redefined due to the Theory of Special Relativity P.S. I also feel as though this is the only unit which can actually change in regards to the Theory of Special Relativity!

The Physics Classroom Website Below explains further:

https://www.physicsclassroom.com/mmedia/specrel/lc.cfm

I hope this helps and please take my response with a grain of salt

Coolmate

Hi blyatman and Coolmate!

Thank you so much for your help.

I completely agree with your logic, however I have just checked the 'official' answer and they suggest that it is C - mass.

I understand that in accordance with Einstein's first and second postulates, length, time and mass are all subject to relativistic effects - however do you have any idea as to why the answer could possibly be mass instead of length?