HSC Physics Question Thread

[beau77bro]

Hi, I'm having trouble with this question. I don't quite understand how we're meant to figure this out.

G-force is described as a reactionary force - it's perceived weight, and we know how much we way from how hard we press against the floor. so here we would feel the heaviest at Q in the same way we would feel weightless at S, because at Q you are experiencing an acceleration change where the floor begins to push and move upwards, whilst you still have the tendency to go down(inertia) as such you feel the heaviest at the bottom. think of it as opposites, your weightless at the top (for the reverse reasons), heaviest at the bottom.

hope this helps goodluck with trials

[kdawgs]

MEDICAL PHYSICS Q could someone please explain t1 and t2 relaxation times? Specifically these statements from my textbook:
"Different tissues will have different T1 relaxation profiles or times. Large molecules and bound water molecules such as in the fat, liver and spleen have a short T1, while free water has a long T1."

 "There are also different T2 profiles. Large molecules found in tendons and muscles have a short T2 while free water has a long T2 "

I don't understand how or why there is a difference in the relaxation times for t1 and t2 depending on the molecule.

[winstondarmawan]

Hello! For the graph of a superconductor (Temp vs Resistance), which shape would be correct?
http://www.globalspec.com/ImageRepository/LearnMore/20153/superconductorbfc636ad4cee4704a85293b4e06adccb.gif
OR
https://scontent-syd2-1.xx.fbcdn.net/v/t34.0-12/20643641_1291020447690142_1176167503_n.png?oh=22447a29bb4a5af096c3c7575b4960d9&oe=598732E4
And also this question here:
https://scontent-syd2-1.xx.fbcdn.net/v/t34.0-12/20624073_1290386117753575_703406917_n.png?oh=07844f7c72598c6beb20572cb88b4fa3&oe=598846B3
TIA!

[12carpim]

Please help!! I cant seem to get the answer right mine was off by 10000???
Thank you!

[jakesilove]

MEDICAL PHYSICS Q could someone please explain t1 and t2 relaxation times? Specifically these statements from my textbook:
"Different tissues will have different T1 relaxation profiles or times. Large molecules and bound water molecules such as in the fat, liver and spleen have a short T1, while free water has a long T1."

 "There are also different T2 profiles. Large molecules found in tendons and muscles have a short T2 while free water has a long T2 "

I don't understand how or why there is a difference in the relaxation times for t1 and t2 depending on the molecule.

Hey! I wouldn't try to understand this point to any sort of high degree. Basically, it comes down to different quantum properties. Whilst you're probably imagining relaxation time as just an electron point one way, and then flipping around in a different direction, there are in reality a number of different impacts that a magnetic field has on a precessing Hydrogen atom.

T1 is just the time taken for one component to flip back, and T2 is just the time taken for another component to flip back. I wouldn't try to understand anything else.

[jakesilove]

Hello! For the graph of a superconductor (Temp vs Resistance), which shape would be correct?
http://www.globalspec.com/ImageRepository/LearnMore/20153/superconductorbfc636ad4cee4704a85293b4e06adccb.gif
OR
https://scontent-syd2-1.xx.fbcdn.net/v/t34.0-12/20643641_1291020447690142_1176167503_n.png?oh=22447a29bb4a5af096c3c7575b4960d9&oe=598732E4
And also this question here:
https://scontent-syd2-1.xx.fbcdn.net/v/t34.0-12/20624073_1290386117753575_703406917_n.png?oh=07844f7c72598c6beb20572cb88b4fa3&oe=598846B3
TIA!

Definitely use that first diagram.

As for the train question, note that the train must be accelerating to the left. If it were not, the ball should hang straight down, as the train would be in an inertial frame of reference.

So, since the train is accelerating to the left, if the string snaps the train will accelerate underneath the ball. So, it will move in a parabolic path downwards! Just think about the physical system, wave your arms around to try and understand it, and draw some diagrams

[jakesilove]

Please help!! I cant seem to get the answer right mine was off by 10000???
Thank you!

The information we have is






First, we always just look at the formulas and see if there's anything we can do. We can find an equation for time in terms of V, using the x-displacement equation





Now, we can use the y-displacement equation.




Since we know theta, this is an equation with only V in it! Solve for V, and we have our answer

[12carpim]

Thank you so much Jake!! You are a  bloody legend!!

[armtistic]

In HSC physics, given the formula R^3/T^2 = GM/4n^2. What is the unit for the period of orbit (T)? Is it seconds or hours or?

[winstondarmawan]

In HSC physics, given the formula R^3/T^2 = GM/4n^2. What is the unit for the period of orbit (T)? Is it seconds or hours or?

Everything in physics is done in SI, so T would be seconds.

[johnk21]

In HSC physics, given the formula R^3/T^2 = GM/4n^2. What is the unit for the period of orbit (T)? Is it seconds or hours or?

Strictly speaking in the HSC you should be using SI units, which in this case is seconds for time.
However, as keplers third law is moreso a RATIO, you can technically use and unit you put in. BUT by doing this you will get out that same unit.
e.g. if you put in time as hours, you get time out as hours if you are using the ratio of r^3/T^2 to find out periods and times of orbits around the same central body.

[winstondarmawan]

Hello! Just need to check my answers (school paper has no solutions) for a few and need help for some others.
https://scontent-syd2-1.xx.fbcdn.net/v/t34.0-12/20631453_1291219204336933_771762729_n.png?oh=3373f6650396286eadf8c642e1f77b6b&oe=598705C8 Is A correct?
https://scontent-syd2-1.xx.fbcdn.net/v/t35.0-12/20641460_1291217984337055_1025674672_o.png?oh=ebb05b043ab41190e96945d1a4eab658&oe=59870D2C Is C correct?
https://scontent-syd2-1.xx.fbcdn.net/v/t34.0-12/20668463_1291218114337042_1787689365_n.png?oh=ab15922147f31c0a11bddfa516dc91a9&oe=598846A6 Part (ii)
https://scontent-syd2-1.xx.fbcdn.net/v/t34.0-12/20668800_1291218261003694_586126526_n.png?oh=73f0df31101a4473339671d484db98ee&oe=598718B7 This would decrease output right? But I'm not too sure.
https://scontent-syd2-1.xx.fbcdn.net/v/t34.0-12/20631433_1291218487670338_710447928_n.png?oh=0104b363734be13cf451f8a1c2e33299&oe=59885469 Part (ii)
Thanks in advance!

[blasonduo]

Hello!

Yes, I believe you are correct for Question 1, the further object will have a higher gravitational potential energy. Even though P is half the altitude of Q, It is not half the potential energy. This is due to the ratio being measured from the centre of the Earth, and thus the ratio is not 1:2.

For 2, Yes! I believe this is correct, fewer vibrations, the less the Cooper pairs break up, and temperatures reduce this!

For 3, Since an increase of Voltage increases the electric field (E = V/d) and the force of the electron is dependant on the Electric field (F = Eq) There will be a greater force on this electron. So for the diagram, as the force is greater, the parabolic motion will be smaller.

For 4, my understanding was that radial magnets gave a smoother output signal, as torque is always at a maximum as the angle between the plane of the coils and the magnetic field is constant. This will INCREASE efficiency, not decrease it

For 5, Faraday's law is heavily reliant on a CHANGE in magnetic flux, the faster the change, the more current is induced. As they are moving it very slowly, there is a much lower change in flux, and thus the lightbulb does not light up.

Hope this helped Goodluck with your studies!

[winstondarmawan]

Hello!

For 3, Since an increase of Voltage increases the electric field (E = V/d) and the force of the electron is dependant on the Electric field (F = Eq) There will be a greater force on this electron. So for the diagram, as the force is greater, the parabolic motion will be smaller.

For 4, my understanding was that radial magnets gave a smoother output signal, as torque is always at a maximum as the angle between the plane of the coils and the magnetic field is constant. This will INCREASE efficiency, not decrease it

For 5, Faraday's law is heavily reliant on a CHANGE in magnetic flux, the faster the change, the more current is induced. As they are moving it very slowly, there is a much lower change in flux, and thus the lightbulb does not light up.

Hope this helped Goodluck with your studies!

For 3, would the range be affected?
For 4, I was thinking that since it was a radial magnetic field their would be a less change in flux, and thus a smaller output. I know with a motor torque increases but this Q isn't looking at speed of rotation..
For 5, wouldn't it just be a smaller flash? I don't get why there is no flash at all
Anyways, thanks for your response! And sorry for being so inquisitive lol

[blasonduo]

For 3, would the range be affected?
For 4, I was thinking that since it was a radial magnetic field there would be a less change in flux, and thus a smaller output. I know with a motor torque increases but this Q isn't looking at speed of rotation.
For 5, wouldn't it just be a smaller flash? I don't get why there is no flash at all
Anyways, thanks for your response! And sorry for being so inquisitive lol

When you say range, do you mean the horizontal distance travelled by the electron? If so, YES! As force is greater, it will reach the plate sooner, and thus  will not travel as far.

If torque increases, there will be a faster change in flux right? This faster change in flux will produce more current!

It COULD be, depending on how slow it is going, most light bulbs won't light up with only 0.005 Volts!

Hope that clears it up