HSC Physics Question Thread

[DrDusk]

Maths Extension 2 always had me sweating every exam, can't give any advice on that when I would freak out myself haha.

That's good to hear that you went well. Well I hope you achieve what you want!.

This is what I expected. NESA added 50 more formulas but still everything is just subbing into formulas, which is like what a 4u student says when they see a 2u paper. Sadly this wont ever change unless they add calculus..

Anyway best of luck for the rest of your trials. Now go on get back to studying.

Oh and IF you can I would love to see the paper. I'm quite interested in how it would look for the peeps this year.

[not a mystery mark]

Maths Extension 2 always had me sweating every exam, can't give any advice on that when I would freak out myself haha.

That's good to hear that you went well. Well I hope you achieve what you want!.

This is what I expected. NESA added 50 more formulas but still everything is just subbing into formulas, which is like what a 4u student says when they see a 2u paper. Sadly this wont ever change unless they add calculus..

Anyway best of luck for the rest of your trials. Now go on get back to studying.
[/quote

It hurts me that we can't use calculus in physics ahaha. Bro, I'm too scared to even use the quadratic formula in physics. Anyways, I shall get some rest for this exam :'') Goodnight man - will keep you updated with any cool physics questions or something else related.
Cheers again!!

[Coolmate]

Hi everyone,

Would someone please be able to step me through this question based on Snell's Law (file attached), I am a bit confused about Snell's Law and how to go about this question, thanks.

Cheers Coolmate

[DrDusk]

4)
a)
For this recall the formula that for light:


b)
The angle of incidence is taken as the angle the light ray makes with the normal. Now if its parallel to the normal, what would this angle be?

c)





d)
In terms of interpretation. Remember before I said that if it's parallel to the normal the angle is zero? Apply the same thing here. It basically means the light ray does NOT refract, because before it was travelling at 0 degrees, and it's still at 0 degrees with respect to the normal.

[Coolmate]

4)
a)
For this recall the formula that for light:


b)
The angle of incidence is taken as the angle the light ray makes with the normal. Now if its parallel to the normal, what would this angle be?

c)





d)
In terms of interpretation. Remember before I said that if it's parallel to the normal the angle is zero? Apply the same thing here. It basically means the light ray does NOT refract, because before it was travelling at 0 degrees, and it's still at 0 degrees with respect to the normal.

Hey DrDusk!

Thanks so much for your help! I understand it now and can do it. I was just wondering though whether the answer for 4a) would be a long number?; because I got an answer of, 2_x10⁸, is this correct?

Thanks again

Coolmate 

[redpanda83]

Hey DrDusk!

Thanks so much for your help! I understand it now and can do it. I was just wondering though whether the answer for 4a) would be a long number?; because I got an answer of, 2_x10⁸, is this correct?

Thanks again

Coolmate 

looks correct

[Coolmate]

looks correct

Cheers 

[mani.s_]

Hi, can someone explain the concept of Entropy to me??? It's very abstract and confusing.

[blyatman]

Hi, can someone explain the concept of Entropy to me??? It's very abstract and confusing.

Google/wikipedia is your friend, and should be your first go to if you haven't already.

Entropy is typically interpreted as a measure of disorder (I'm not familiar with the new physics syllabus, but I would imagine that's probably all you'd need to know). There's a formula for it on wiki, but I doubt you'd ever need to use it unless you're taking a course on molecular gas dynamics or something similar. Basically, the second law of thermo states that entropy can never decrease, which limits the reactions and procceses that can occur.

[classof2019]

Can someone please explain what happens to the total energy of a satellite when it moves from a higher to lower orbit?

I understand that kinetic energy increases and potential energy decreases, but after doing a practice question the solution suggested that total energy also decreases - why is this the case?

Thank you.

[DrDusk]

In theory yeah KE increases and Potential energy decreases, leading to energy conservation. However in reality the satellite must fire retrograde rockets(rockets in the opposite direction) to descend to a lower orbit which decrease the KE. So technically some KE is lost.

In calculation questions though you don't need to consider the effect of the retrograde rockets.

[classof2019]

In theory yeah KE increases and Potential energy decreases, leading to energy conservation. However in reality the satellite must fire retrograde rockets(rockets in the opposite direction) which decrease the KE at the higher level orbit. So technically some KE is lost.

In calculation questions though you don't need to consider the effect of the retrograde rockets.

Thanks!
Just a q, are the mechanics behind orbital transfer a part of the new syllabus? Do we need to know how rockets transition between orbits or must we only perform calculations? Cause I've found no mention of it in numerous textbooks, yet the Excel book goes into it in quite some detail.

[DrDusk]

The HSC syllabus does have a section which asks you to qualitatively describe orbital motions and what not, so yes you should know it all

[DrDusk]

Can someone please explain what happens to the total energy of a satellite when it moves from a higher to lower orbit?

I understand that kinetic energy increases and potential energy decreases, but after doing a practice question the solution suggested that total energy also decreases - why is this the case?

Thank you.

Also another thing to note is that the value of 'g' is not constant as the satellite will usually undergo a large change in orbital radius. So you technically can't say that the Energy of the satellite is conserved.

[classof2019]

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