HSC Physics Question Thread

[conic curve]

In GPE questions when it asks "calculate the energy________" what are they asking?

Also when they ask for "change in GPE" how do you do those types of questions, I never got them

[ml125]

In GPE questions when it asks "calculate the energy________" what are they asking?

Also when they ask for "change in GPE" how do you do those types of questions, I never got them

If it was something like "Calculate the energy required to lift an object from height x to height y," you would need to calculate GPE at points x and y, then find the difference between these two values. This is basically a "change in GPE" question - just need to find two separate values for GPE depending on the scenario given in the question then subtract. It would help if there was a specific question you had in mind so we could explain it more clearly.

[jakesilove]

If it was something like "Calculate the energy required to lift an object from height x to height y," you would need to calculate GPE at points x and y, then find the difference between these two values. This is basically a "change in GPE" question - just need to find two separate values for GPE depending on the scenario given in the question then subtract. It would help if there was a specific question you had in mind so we could explain it more clearly.

Spot on

[samuels1999]

Hi Jake,

Regarding year the 12 Physics course, I just wanted to know: is a student that does Chemistry advantaged over a student who doesn't in certain topic areas?

Thanks,
Samuel

[RuiAce]

Hi Jake,

Regarding year the 12 Physics course, I just wanted to know: is a student that does Chemistry advantaged over a student who doesn't in certain topic areas?

Thanks,
Samuel

Chemistry and physics are 97% distinct in what is taught. The advantage that a chemistry student has over a physics student is minimal. In fact, for the crossover between galvanic cells and cathode ray tubes, it causes more confusion arguably.

There is a tiny benefit in that a chemist will have an immediate understanding of valence and conduction bands in semiconductors from considering valence electrons in Year 11. It also helps at the point of some options, where chemists will be better adapted to the nuclear chemical equations.

[jakesilove]

Hi Jake,

Regarding year the 12 Physics course, I just wanted to know: is a student that does Chemistry advantaged over a student who doesn't in certain topic areas?

Thanks,
Samuel

Very little advantage, and definitely nothing to worry about

[pels]

Very little advantage, and definitely nothing to worry about

As both a Chemistry and Physics student this year, it was at first confusing as in Physics its the positive current flow that starts from the positive ANODE, whereas in Chemistry its the negative current flow starting from the negative ANODE, but there is not much advantage I would say, other than if you do the Option Topic: From Quanta To Quarks as I currently am, and a small amount in From Ideas To Implementation, as you go over emission spectra and the atom, which is closely studied in Chemistry

[WyattRey]

Hi everyone,

Could someone explain to me why the relaxation time for hydrogen in different molecules differs? For example in water it would be longer than fat, etc. An answer I'm looking at says "Hydrogen in water has a longer relaxation time because the interaction with its surroundings (water) is small. The relaxation time of hydrogen in other molecules is shorter because it has greater interactions with its surroundings". I feel this is quite vague, even if its probably all you need to write.

Thanks 

[pels]

Hi everyone,

Could someone explain to me why the relaxation time for hydrogen in different molecules differs? For example in water it would be longer than fat, etc. An answer I'm looking at says "Hydrogen in water has a longer relaxation time because the interaction with its surroundings (water) is small. The relaxation time of hydrogen in other molecules is shorter because it has greater interactions with its surroundings". I feel this is quite vague, even if its probably all you need to write.

Thanks 

What sort of question are you answering?

[jakesilove]

Hi everyone,

Could someone explain to me why the relaxation time for hydrogen in different molecules differs? For example in water it would be longer than fat, etc. An answer I'm looking at says "Hydrogen in water has a longer relaxation time because the interaction with its surroundings (water) is small. The relaxation time of hydrogen in other molecules is shorter because it has greater interactions with its surroundings". I feel this is quite vague, even if its probably all you need to write.

Thanks 

Hey! To be honest, I would probably stick to the answer you've described, because I'm not able to explain it in any more real detail. Personally, I always understood the relaxation time as dependent on the number of Hydrogen atoms present in a given area, rather than the way they interact with their surroundings. Needless to say, this is an extremely complicated area of Physics, and not one you need to know it great depth (other than in an explanatory sense). Sorry that I can't give you more detail!

Jake

[Neutron]

That feel when you still don't really understand how you know which time is the dilated one and which time is the proper one.. Pls help with this question

A scientist at a particle accelerator laboratory observes the lifetime of a particular subatomic particle to be 1.0 x 10^-6 s when it is travelling at 0.9999c. What would the lifetime of the particle be if it were stationary in the laboratory?

Cheers

[RuiAce]

That feel when you still don't really understand how you know which time is the dilated one and which time is the proper one.. Pls help with this question

A scientist at a particle accelerator laboratory observes the lifetime of a particular subatomic particle to be 1.0 x 10^-6 s when it is travelling at 0.9999c. What would the lifetime of the particle be if it were stationary in the laboratory?

Cheers

Might wanna look at posts #928 and #929.

So using "common sense and logic" as we call it, I'd say that time dilates when the particle is moving, so it's lifetime is longer then. When it's at rest, it's lifetime should be shorter.

So we just sub the one in that will make it smaller

[Neutron]

Might wanna look at posts #928 and #929.

So using "common sense and logic" as we call it, I'd say that time dilates when the particle is moving, so it's lifetime is longer then. When it's at rest, it's lifetime should be shorter.

So we just sub the one in that will make it smaller

Yep that definitely makes sense but I think all this fatigue has gotten to my head. So with the particle moving, isn't it only in its reference frame where time dilates? So I'm using the example of like a spacecraft flying past the Earth, only the time on the spacecraft has dilated, the time on Earth is still proper. So using that logic, wouldn't the scientist's time be proper? Sorry if this is hella dumb :/

Neutron

[Neutron]

One more thing, with this 8marker from 2010, I have absolutely no idea how to approach it, if you guys could perhaps give a dot point outline (or if you have time, a response ) on what I'm supposed to cover, that would be absolutely amazing!

Two significant problems that will affect a manned spaceflight to Mars are:
-the changes in gravitational energy
-protecting the space vehicle from high-speed electrically charged particles from the Sun
Use your understanding of physics to analyse each of these problems.

Thankfully this isn't in the 2016 paper otherwise it would be 8 marks out the window! Rip

Neutron

[Spencerr]

One more thing, with this 8marker from 2010, I have absolutely no idea how to approach it, if you guys could perhaps give a dot point outline (or if you have time, a response ) on what I'm supposed to cover, that would be absolutely amazing!
Two significant problems that will affect a manned spaceflight to Mars are:
-the changes in gravitational energy
-protecting the space vehicle from high-speed electrically charged particles from the Sun
Use your understanding of physics to analyse each of these problems.
Thankfully this isn't in the 2016 paper otherwise it would be 8 marks out the window! Rip
Neutron

Hi, I'll try answer this the best I can, splitting the question into 2 parts for 4 marks each.

Changes in gravitational energy
- Gravitational potential energy is defined as -GmM/R, therefore as the rocket LEAVES Earth, it's gravitational energy increases. However, the law of conservation of energy (dictating that the total energy in a closed system is constant), suggests that energy must come from another source. This other source is the Kinetic energy / chemical energy within the fuel of the rocket. As the rocket leaves Earth, the KE of the rocket decreases (increasing GPE). This is a problem. In order to maintain the level of KE and increase the velocity of the rocket, more fuel must be burnt and used up. This involves the firing of rocket boosters to provide a constant thrust for the rocket.
- When the rocket enters the G field of Mars, the reverse situation happens. It begins to accelerate, being attracted by the gravity of the planet, towards the surface. As a result of its acceleration, it converts GPE to KE very quickly, losing altitude but gaining heat (from friction) and velocity. (Law of conservation of energy). This again is a problem as a velocity too high is difficult to control, and may be fatal for the probe/occupants inside. In order to solve this problem, rocket boosters are fired in the opposite direction to slow the descent of the probe, reducing its KE as it's GPE decreases.

High Speed Electrical charged Particles
- High speed electrically charged particles coming from the sun are often come from solar flares (where the sun emits a burst of solar radiation). They are quite problematic as they can damage sensitive equipment within the spacecraft and also penetrate through the walls of the spacecraft, damaging other parts inside and may be harmful for the occupants. Alongside causing damage, these charged particles interfere with communication (much like the situation of an ionisation blackout in re-entry), which is another problem.
- In order to solve this problem, the outer layer of the spacecraft can be coated with a material which can be electrically charged to repel these high speed charged particles. Insulating material which prevents these particles from penetrating into the spacecraft can also be applied. Furthermore, communication signals can be sent from the backend or the spacecraft (or whichever end isn't being exposed to these high speed charged particles).

I hope thats enough to get 7 marks at least haha but that's my attempt