HSC Physics Question Thread

[RuiAce]

Could you please show worked solutions so we know how to actually get the answer, after trying for ages?

Refer to posts #990 and #991

[Wales]

Not sure if this is the appropriate place to post, let me know if it isn't

So throughout the year I've been struggling quite hard in Physics. I've been recommended to drop by my teacher multiple times and yesterday I just received my results for the pendulum test. My result was less then satisfying with a mere 40% in last weighing 20% overall. Should I continue my investment in Physics? Will the failure of this test affect my overall ranking that hard? I came last place. 

Is the upcoming physics module extremely challenging? I'm currently on 13 units and enjoying Physics but just can't seem to get it well enough. If I drop I will be left with 11 units. Would it be worth continuing Physics if my mark won't be that great? My teacher tells me the time I need to spend would be far too much and it would be better to drop it and focus on my other subjects. Will post them if needed.

Regards, Wales

[RuiAce]

Not sure if this is the appropriate place to post, let me know if it isn't

So throughout the year I've been struggling quite hard in Physics. I've been recommended to drop by my teacher multiple times and yesterday I just received my results for the pendulum test. My result was less then satisfying with a mere 40% in last weighing 20% overall. Should I continue my investment in Physics? Will the failure of this test affect my overall ranking that hard? I came last place. 

Is the upcoming physics module extremely challenging? I'm currently on 13 units and enjoying Physics but just can't seem to get it well enough. If I drop I will be left with 11 units. Would it be worth continuing Physics if my mark won't be that great? My teacher tells me the time I need to spend would be far too much and it would be better to drop it and focus on my other subjects. Will post them if needed.

Regards, Wales

The question then becomes what drives you to enjoy physics despite its apparent difficulty?

Most people are often put off by the difficulty of something (relative to them). The HSC is about doing what you like, however in general (not always) this implies that you do have some kind of a talent for the course.

When teachers suggest you to drop, they're probably right. Teachers cannot ever force you to drop, however if they're providing pressure then it's probably for the better. Of course, that pressure can be rejected though; I know people who have done so.

So the main question is, what is pushing your like for physics? What is this powerful force that pushes for you to not drop? Or is there something about the course itself or how it's taught that you like?
Then, contrast that to both the how and why behind your marks. What do you put into physics, and what do you suspect is causing it to not pay off? A good starting point would be to identify where the marks were lost first, and what you could've done instead.

(Units wise: I did 10 units, yet I know people who did 16. That's your own call.)

Of course, note that it also depends on your performance in physics relative to your performance in everything else as well. If there's some subject creating even more difficulty than this then that should probably be addressed first.

[samuels1999]

Hi Guys,

I have two questions regarding Mass Dilation in Special Relativity:
Firstly, Does Mass Dilation have anything to do with E=mc^2?
Secondly, When mass increases...according to the definition of mass...there should be more matter in the object. I just want to clarify.. do individual atoms gain more mass? or is there more matter in the object all together at high speeds?

Sorry part 2 is terribly worded.

Thanks
Samuel

[jamonwindeyer]

Hi Guys,

I have two questions regarding Mass Dilation in Special Relativity:
Firstly, Does Mass Dilation have anything to do with E=mc^2?
Secondly, When mass increases...according to the definition of mass...there should be more matter in the object. I just want to clarify.. do individual atoms gain more mass? or is there more matter in the object all together at high speeds?

Sorry part 2 is terribly worded.

Thanks
Samuel

Hey Sam!

1. Yes. Consider an object travelling super close to the speed of light. If we keep doing work on that object, it will keep accelerating, and thus eventually reach the speed of light. What if we then did more work on the object? Well, its kinetic energy must increase, we are doing work after all. But the speed cannot exceed the speed of light. Since \(KE=\frac{1}{2}mv^2\), the only option is for the mass to increase. Work (energy) has been converted into mass (!!), and the ratio is given by \(E=mc^2\)

2. The issue here is the difference between invariant mass and relativistic mass. Invariant mass is our typical understanding of mass, the amount of matter in the object. Relativistic mass is to do with the velocity of the observer, it is different and we don't look at it in the same way. So to answer your question, there are no atoms added to our object. We measure the same amount of atoms to be heavier.

Note, the terminology in my second answer is not assessable, and neither is a super precise explanation of the phenomena

[jakesilove]

Hey Sam!

1. Yes. Consider an object travelling super close to the speed of light. If we keep doing work on that object, it will keep accelerating, and thus eventually reach the speed of light. What if we then did more work on the object? Well, its kinetic energy must increase, we are doing work after all. But the speed cannot exceed the speed of light. Since \(KE=\frac{1}{2}mv^2\), the only option is for the mass to increase. Work (energy) has been converted into mass (!!), and the ratio is given by \(E=mc^2\)

2. The issue here is the difference between invariant mass and relativistic mass. Invariant mass is our typical understanding of mass, the amount of matter in the object. Relativistic mass is to do with the velocity of the observer, it is different and we don't look at it in the same way. So to answer your question, there are no atoms added to our object. We measure the same amount of atoms to be heavier.

Note, the terminology in my second answer is not assessable, and neither is a super precise explanation of the phenomena

Just to add to your answer to the second question; I think this basically brings to light the typical terminological issue that arises when talking about something like mass. Mass is a descriptor; something has a mass of X. That describes the object, at a particular point in time and space. When something moves at high speeds, it gains mass, because energy is ABSOLUTELY EQUIVALENT to mass. That's what E=mc^2 means; as energy increases, so too does mass. Why do higher speeds cause greater mass? Because energy is mass, so obviously more energy means more mass. It really is a very complicated area of physics, made even more complicated by terminology like 'relativistic mass' etc. If you're interested, check out a great video here. However, to reiterate Jamon's point, none of this is important in your HSC!

[katnisschung]

Think the answers from surfing are correct.

delta(x) = vtcos(40) = 300 - so, by rearranging, t = 300/(vcos(40)) when the range is achieved (when the ball hits the ground).

Then, sub this value of t into the the quadratic for delta(y) of form - delta(y) = -1/2at^2 + vsin(40) + 218.7

Allowing this quadratic to be = to 0 (as, when the ball has achieved the range of 300m, the vertical displacement of the projectile will be 0 (or -218.7m; depending on how you set up the quadratic initially)) proceed to solve for 'v'.

I had v^2 = 1597.481175... so v = 39.96850228
so uy = vsin(40) = 39.97 x sin(40) = 25.69 m/sec
and ux = vcos(40) = 39.97 x cos(40) = 30.62 m/sec

Then, for the time of flight, I just subbed the aforementioned 'v' back into the initial quadratic for delta(y), letting it = 0 (i.e. delta(y) = 0 since when the time of flight is achieved, the projectile reaches the ground); solving it with the quadratic formula.

You should get two values for t (the positive value being the one you want as t>0), one of them being 9.798270249... secs.

Hope this helps.

thanks and.....
i'm a little confused...
at the beginning why did u take delta(x) = vtcos(40) = 300 instead of
delta(x) = utcos(40) = 300

[RuiAce]

thanks and.....
i'm a little confused...
at the beginning why did u take delta(x) = vtcos(40) = 300 instead of
delta(x) = utcos(40) = 300

Probably was a typo but it doesn't matter here (fortunately).

Note that u_x=v_x

[katnisschung]

haha can somebody explain the steps to get u
(im really bad at maths and the quadratics are confusing the hell out of me)

(this is in reference to a question i posted ages answered by and)

[jamonwindeyer]

haha can somebody explain the steps to get u
(im really bad at maths and the quadratics are confusing the hell out of me)

(this is in reference to a question i posted ages answered by and)

Hey Katniss! I'll start from this line:



So, we now know how long the projectile was in the air. We also know that AFTER this amount of time, its vertical displacement is 218.7 metres below the origin. So we use \(\Delta y=u_yt+\frac{1}{2}at^2\) from our reference sheet, where \(u_y=u\sin{40}\):



Notice that going into that second line, the \(u\) on the top and bottom of that first fraction cancel out! So the excellent thing about this quadratic is that there is no formula required! Keep rearranging to find:



I know it looks bad, but it is just moving things around in your expression! This formula will let you get an expression of the form \(\frac{1}{u^2}=??\), and then you just rearrange this to get your final answer!

If you are having trouble visualising how the algebra itself takes place, try replacing the \(\sin{40}\) and \(\cos{40}\) with numbers earlier in the problem and using a rounded version!



Using the numbers instead, and simplifying and rounding as you go, may help you! It's not as correct as using the real thing all the way through, but it's close!

[katnisschung]

thanks Jamon i finally get it!

[Wales]

The question then becomes what drives you to enjoy physics despite its apparent difficulty?

Most people are often put off by the difficulty of something (relative to them). The HSC is about doing what you like, however in general (not always) this implies that you do have some kind of a talent for the course.

When teachers suggest you to drop, they're probably right. Teachers cannot ever force you to drop, however if they're providing pressure then it's probably for the better. Of course, that pressure can be rejected though; I know people who have done so.

So the main question is, what is pushing your like for physics? What is this powerful force that pushes for you to not drop? Or is there something about the course itself or how it's taught that you like?
Then, contrast that to both the how and why behind your marks. What do you put into physics, and what do you suspect is causing it to not pay off? A good starting point would be to identify where the marks were lost first, and what you could've done instead.

(Units wise: I did 10 units, yet I know people who did 16. That's your own call.)

Hey Rui I didn't expect to see you here. I remember you being part of the accellerated classes at my school a few years back, the Math genius as most people refer to you haha.

Well, I rather enjoy Physics because of the fine detail contained within the course and understanding how, why and what allows something to work. Currently doing the Space module and I'm loving it.

I guess it comes down to whether I'm going to be dedicated enough. When it comes down to raw talent I feel like Physics just doesn't suit me. My 11 Yearly's mark was atrocious and I've only done well in the Practicals up until this point. I feel like what's causing my performance in Physics is the pace the class is going at and I feel like I'm unable to keep up a majority of the time, it's a class of 14 so it's relatively small. A big factor in why I want to drop right now is that I've already botched my Term 1 assessment worth 20% and I know that I won't be able to bring it up due to the nature of the students in the class, at least not to a satisfactory level. I'm taking Ext 2 maths as well so I've considered spending the time freed by Physics in that (Not everyone is as talented as you Rui )

I've got a few days to think it over so let me know you're suggestion but basically I'm struggling really hard consistently and I've been told it's not the course for me by my teacher multiple times ( Since term 2 last year ) and I feel that she is right.

[RuiAce]

Hey Rui I didn't expect to see you here. I remember you being part of the accellerated classes at my school a few years back, the Math genius as most people refer to you haha.

Well, I rather enjoy Physics because of the fine detail contained within the course and understanding how, why and what allows something to work. Currently doing the Space module and I'm loving it.

I guess it comes down to whether I'm going to be dedicated enough. When it comes down to raw talent I feel like Physics just doesn't suit me. My 11 Yearly's mark was atrocious and I've only done well in the Practicals up until this point. I feel like what's causing my performance in Physics is the pace the class is going at and I feel like I'm unable to keep up a majority of the time, it's a class of 14 so it's relatively small. A big factor in why I want to drop right now is that I've already botched my Term 1 assessment worth 20% and I know that I won't be able to bring it up due to the nature of the students in the class, at least not to a satisfactory level. I'm taking Ext 2 maths as well so I've considered spending the time freed by Physics in that (Not everyone is as talented as you Rui )

I've got a few days to think it over so let me know you're suggestion but basically I'm struggling really hard consistently and I've been told it's not the course for me by my teacher multiple times ( Since term 2 last year ) and I feel that she is right.

Aha hey hey Well I'm not even close to being the smartest math person I know anymore. Nice seeing someone from that school here

Well that's a good thing to have no doubt about it; an actual interest in what you're learning. But then if you were to keep physics then this interest needs to push you on to actually ensuring you don't fall behind. It's normal for things to not come to you the very instant you're taught it, however if it takes a bit too long for that to happen then something else is up. It could possibly be that your brain isn't well versed against the concepts taught, but that I can't say for sure - only you'd be able to explain how you're falling behind

(I did put heaps of time into MX2 though. I didn't rely on talent 100%)

That being said, if you do start to feel your teacher's right you may want to just drop it then. The HSC is a game; gotta find the option with the better pay-off and judging by what you said, it might be the better choice. So I'm not going to give an instruction but my recommendation would probably be drop as well

[Wales]

Aha hey hey Well I'm not even close to being the smartest math person I know anymore. Nice seeing someone from that school here

Well that's a good thing to have no doubt about it; an actual interest in what you're learning. But then if you were to keep physics then this interest needs to push you on to actually ensuring you don't fall behind. It's normal for things to not come to you the very instant you're taught it, however if it takes a bit too long for that to happen then something else is up. It could possibly be that your brain isn't well versed against the concepts taught, but that I can't say for sure - only you'd be able to explain how you're falling behind

(I did put heaps of time into MX2 though. I didn't rely on talent 100%)

That being said, if you do start to feel your teacher's right you may want to just drop it then. The HSC is a game; gotta find the option with the better pay-off and judging by what you said, it might be the better choice. So I'm not going to give an instruction but my recommendation would probably be drop as well

I'm rather torn. I would love to pursue Physics and get a grasp of what it really is however I feel the investment is far too great for my current position. Maybe I could continue that later in Uni or something along those lines. Right now I think the better choice may be to drop it and dedicate myself to my remaining subjects. Everybody keeps telling me that the teacher cannot force me out and I agree but I think it's at that point where she essentially believes that in my best interests it would be best to drop. I will think over it again but the likely conclusion is that I will indeed drop it.

Thank you for your thoughts and insight. It is greatly appreciated

Regards, Wales

[jamonwindeyer]

I'm rather torn. I would love to pursue Physics and get a grasp of what it really is however I feel the investment is far too great for my current position. Maybe I could continue that later in Uni or something along those lines. Right now I think the better choice may be to drop it and dedicate myself to my remaining subjects. Everybody keeps telling me that the teacher cannot force me out and I agree but I think it's at that point where she essentially believes that in my best interests it would be best to drop. I will think over it again but the likely conclusion is that I will indeed drop it.

Thank you for your thoughts and insight. It is greatly appreciated

Regards, Wales

As a side note; HSC Physics is majorly different to what studying Physics at uni is like. At uni it is much more mathematical, a lot more rigorous, much more detailed! That appeals to a lot of people but it turns a lot of people off also

HSC Physics is a fantastic course for a lot of reasons (and a bad one for a few). It's got fascinating content that gives you a cool understanding of many aspects of the world around you. But it is tough, there is no denying that.

I'm always of the belief that you should stick with what you enjoy. That said, this is the HSC, and if you are consistently falling short of your goals then that will eat away at your enthusiasm over time. If you are the kind of person who can stay optimistic and keep working hard, then I'd be keeping Physics around, perhaps even until Half Yearlies (which is the latest anyone should drop anything imo)? it just sounds like you really love it, and I hate seeing people drop something they love just because they aren't quite getting where they want to be. I know it sucks, but hey, the HSC isn't just about marks right? It's about learning things that excite and motivate you!

Just my two cents. Of course you need to look after yourself and keep your other subjects travelling nicely; only you will ultimately know what is in your best interests