HSC Physics Question Thread

[jakesilove]

Hi, for HSC 2005 Q20, when it mentions reliability, in what sense are we meant to respond in? Given that reliability is INCREASED by repetition, it is asking us to "describe how you assessed the reliability of the information you found"; I can only think of accurate source (reliable, i.e. from a scientific institution) at the present moment, but it's worth 6m :/

Reliability of secondary sources is largely about cross-checking your sources; do different sources say the same thing? Does that information correspond with your understanding of the topic area? Go into some depth about sources you used, how you found them, how you analysed them, how many sources you used etc. etc. Basically, make shit up, but I promise you won't get a question that absurd in a modern paper.

[Cindy2k16]

Is this part of an option? Unfortunately, I won't be able to help you out, but hopefully someone else can!

Actually....its in the core 

[jakesilove]

Actually....its in the core 

Well shit.

No, you definitely don't need to know anything about Mars. The 'Change in gravitational energy' can be understood as ANY movement of the rocket, so potentially just talk about rocket launches in as much detail as possible, as well as layers of protection from solar flares etc. Fucking weird question; basically, just spam information about rockets and hope for the best is my advice!

[Brenda0708]

HI I would start by calculating the acceleration the electron experiences inside the electric field. Use F=ma for this, and sub in the force you found in a and the mass of an electron to find a.
Then draw the triangle for the initial velocity to determine the initial horizontal and vertical velocity of the electron at A.
Once you have all these values, you can act as if this is a normal projectile motion question except the acceleration is not 9.8, but the 'a' you calculated.

To find the time taken to travel from A to D, that's basically working out the time of flight. Use the formula starting with 'change in y' (the triangle with 'y' next to it). Sub in the change in y as 0 (since overall, the vertical displacement of the particle from A to D is 0), sub the initial vertical velocity, the acceleration you calculated and then rearrange the equation to find t. One value of t will be 0 (since the particle has 0 vertical displacement at the beginning too) and the other value will be the time it took to reach D.

Hope this helps

Thank you!!!!

[Albertenouttaten]

Hi Cindy, this question requires you to talk about all the changes in potential energy and the consequences of these chagnes. These being:
1) Earth to Earth Orbit
2) Earth Orbit to Sun Orbit then to Mars Orbit
3) Mars Orbit to Mars Surface
4) Mars surface to Mars Orbit
5) Step 2 but in reverse
6) Lowered down to Earth orbit.
Steps 1,2,4 are increases in GPE and the leftover are decreases in GPE. Also talk about g-forces experienced, the need for retroboosters when entering into Mar's atmosphere (retroboosters would be required in this process as the aim is to slow down the ship as the decrease in GPE results in increased kinetic energy and also the ship will be used again to return to Earth hence cannot simply rely only on the blunt shape of the ship and also another aspect you can talk about is that Mar's atmosphere is not as thick as Earth's so atmospheric friction isn't enough of a force to slow the ship down to safe levels)

Second part of the question refers to the charged particles emited from the Sun (KEY NOTE: they are charged particles and not limited to being +ve or -ve). There are two methods of redirecting or protecting the ship, this is through magnetic fields or electric fields. If we use an electric field, it will only repel one type of charge, hence the key note. Therefore we must use an magnetic field to protect the ships equiment from the high velocity particles. This is a very summarised answer and that question would require you to expand on this but these are the general aspects of the quesiton. Definitely encoporate many aspects of the syllabus.

[Brenda0708]

Hi, how I would do this is follow Cindy2k16's way of getting the acceleration from F=ma and getting the y-component of the velocity with the triangle.
But an easier way to do the projectiles part is use v=u+at, where v=-u as this is using the symmetry of the parabolic arc and by using the a from above,
t=-2u/a  [ie t=(-2x6x10^6sin60)/(-1.7587x10^14)]

Hope this helps 

Thank you for your help. What do you mean by the symmetry of the parabolic arc? V= -u as in the vertical component of the final velocity = the negative of the initial velocity? Why? haha :')

[Cindy2k16]

Hi Cindy, this question requires you to talk about all the changes in potential energy and the consequences of these chagnes. These being:
1) Earth to Earth Orbit
2) Earth Orbit to Sun Orbit then to Mars Orbit
3) Mars Orbit to Mars Surface
4) Mars surface to Mars Orbit
5) Step 2 but in reverse
6) Lowered down to Earth orbit.
Steps 1,2,4 are increases in GPE and the leftover are decreases in GPE. Also talk about g-forces experienced.

Second part of the question refers to the charged particles emited from the Sun (KEY NOTE: they are charged particles and not limited to being +ve or -ve). There are two methods of redirecting or protecting the ship, this is through magnetic fields or electric fields. If we use an electric field, it will only repel one type of charge, hence the key note. Therefore we must use an magnetic field to protect the ships equiment from the high velocity particles. This is a very summarised answer and that question would require you to expand on this but these are the general aspects of the quesiton. Definitely encoporate many aspects of the syllabus.

Well shit.

No, you definitely don't need to know anything about Mars. The 'Change in gravitational energy' can be understood as ANY movement of the rocket, so potentially just talk about rocket launches in as much detail as possible, as well as layers of protection from solar flares etc. Fucking weird question; basically, just spam information about rockets and hope for the best is my advice!

Thank you!

[imtrying]

Hey:)
In Medical Physics, is the piezoelectric effect basically when an oscillating potential difference is applied to a piezoelectric crystal it causes vibrations in the lattice of the crystal to give off high frequency sounds, and these are what is used in transducers?

[Cindy2k16]

Hey:)
In Medical Physics, is the piezoelectric effect basically when an oscillating potential difference is applied to a piezoelectric crystal it causes vibrations in the lattice of the crystal to give off high frequency sounds, and these are what is used in transducers?

The piezoelectric effect is how when a potential difference is applied to a piezoelectric crystal, it causes it to deform. And then the other way round too (for ultrasound detection). It doesn't have to be an oscillating potential difference- thats just whats used In ultrasound transducers. It causes the crystal to repeatedly deform at a high frequency so its basically vibrating

[Brenda0708]

So for these kinds of questions, always think: who's moving at relativistic speeds? When moving at such high speeds, recall that you experience time and mass dilation and length contractions. So since you're moving in this question, the length you measure is always shorter than the real length, so we are trying to calculate Lv. (note the real length is stated as a fact in the first sentence and this is Lo).

Hope this helps. 

Waait doesnt the stationary observer see the length of the fast moving object contract in the direction of their velocity? And we measure the real length? but in this case the moving person is measuring the length of something when they are moving so im a bit lost as to whether or not they will see it contract or see its 'real length'

[jakesilove]

Waait doesnt the stationary observer see the length of the fast moving object contract in the direction of their velocity? And we measure the real length? but in this case the moving person is measuring the length of something when they are moving so im a bit lost as to whether or not they will see it contract or see its 'real length'

If any object is moving relative to the observer, the observer will measure the relativistic length! So, if I'm running past you, you will measure my relativistic speed. However, I will think YOU'RE running past ME, so I'll actually be measuring your relativistic speed! Does that clarify things?

[Brenda0708]

If any object is moving relative to the observer, the observer will measure the relativistic length! So, if I'm running past you, you will measure my relativistic speed. However, I will think YOU'RE running past ME, so I'll actually be measuring your relativistic speed! Does that clarify things?

ohhhhhh thank you!

[Albertenouttaten]

If any object is moving relative to the observer, the observer will measure the relativistic length! So, if I'm running past you, you will measure my relativistic speed. However, I will think YOU'RE running past ME, so I'll actually be measuring your relativistic speed! Does that clarify things?

Lol i just wonder how high Einstein was to come up with these thought experiments.

[Cindy2k16]

Just wondering to the people who did hsc physics prior to this year and did well, how did you feel when you finished the exam? Did you know that you had aced it? Were there questions you weren't sure of or did you just totally know everything ?

[jakesilove]

Just wondering to the people who did hsc physics prior to this year and did well, how did you feel when you finished the exam? Did you know that you had aced it? Were there questions you weren't sure of or did you just totally know everything ?

I definitely didn't think I aced the exam. It was a seriously weird paper (2014 was a weird mix of easy and just bloody strange), and so I wasn't hugely confident with my performance. Like, I was sure I did fine, but I definitely didn't think I aced it or anything like that! We're all bad judges of ourselves, so once you walk out of the exam room, you may as well just forget the paper and move on. There's no way to tell what is a good raw mark, and what is a bad raw mark, because you have no idea how the rest of the cohort went. You seem completely ready to smash the exam, and that's all that's important. You'll do great tomorrow