HSC Physics Question Thread

[jakesilove]

more help needed. sorry for being a hassle, but the answers say the wavelength should half for this, even though the speed is kept constant. I disagree, but Im not sure- the amplitude should double but yea

Hey!

If you double the number of turns, then the FORCE doubles. So, the rotor WILL rotate faster, halving the wavelength. Make sense?

[statues]

From the 2016 exam choice trial:
17.
A proton moving at 99.999999% the speed of light has approximately as much kinetic energy as:
a.  a 20g snail moving at 7 mms-1
b 100 kg car moving at 25 ms-1
c. 30 kg child running at 3 ms-1
d. 150 g ball thrown at 14 ms-1

Answer was A.
I don't know how they got it - I plugged the velocity into Einsteins mass dialation equation and then plugged that into the kinetic energy formula but none of them seemed to work out.
Thanks in advance 

[beau77bro]

Hey!

If you double the number of turns, then the FORCE doubles. So, the rotor WILL rotate faster, halving the wavelength. Make sense?

but it says the speed is kept the same? which is my problem.

[jakesilove]

but it says the speed is kept the same? which is my problem.

Ah yep I see; in that case, wavelength would stay the same, as you've mentioned. I would chalk it up to a badly worded/designed question

[jakesilove]

From the 2016 exam choice trial:
17.
A proton moving at 99.999999% the speed of light has approximately as much kinetic energy as:
a.  a 20g snail moving at 7 mms-1
b 100 kg car moving at 25 ms-1
c. 30 kg child running at 3 ms-1
d. 150 g ball thrown at 14 ms-1

Answer was A.
I don't know how they got it - I plugged the velocity into Einsteins mass dialation equation and then plugged that into the kinetic energy formula but none of them seemed to work out.
Thanks in advance 

Hey! So the kinetic energy of the proton will be



Plugging in relevant values, including the mass of the proton, gets us



Then, assuming A) was in mm per second



Which is pretty bloody close to the Proton kinetic energy!

[Mymy409]

they sometimes pop up in trials, like extra content to check your knowledge - usually it's pretty minor understanding though, and I haven't much if any in hscs but Im sure Jake and Jamon have a better idea

ohhh, ive forgotten a lot of prelim stuff. welp, lets hope it doesnt come up in trials

[statues]

Hey! So the kinetic energy of the proton will be



Plugging in relevant values, including the mass of the proton, gets us



Then, assuming A) was in mm per second



Which is pretty bloody close to the Proton kinetic energy!

Hey so I can't get the same value for proton energy. Is this right?
`Ek = 0.5 \times(\frac{1.673\times10^{-27}}{\sqrt{1-0.99999999}})\times(0.99999999\times3\times10^{8})^{2}`

[kiwiberry]

Hey so I can't get the same value for proton energy. Is this right?
`Ek = 0.5 \times(\frac{1.673\times10^{-27}}{\sqrt{1-0.99999999}})\times(0.99999999\times3\times10^{8})^{2}`

The 0.99999999 under the square root needs to be squared, other than that you're all good

[statues]

The 0.99999999 under the square root needs to be squared, other than that you're all good

aahhhhh  tysm

[beau77bro]

help pls. I dont understand

could i get some help on this? the question is very strange - I don't think it gives u enough values but Im not great at medical so more help needed. thanks again guys u r life savers

could i also get help with this Question: i think they used √GM/r  instead √2GM/r

so does that mean its wrong or am I missing something? The answer is A

with the second one the Answer is D - i can't see how u would get there treating the speed of light as 3x10^8

another one - this i get why the answer is A - but shouldn't having the frequency mean you are decreasing the rate of change of magnetic flux? So it shouldn't just double EMF because the input is doubled - but stay the same since the rate was halved?

[katnisschung]

why/how do accelerating charges produce emr?
thanks  (background this is for quanta to quarks)

[jakesilove]

could i get some help on this? the question is very strange - I don't think it gives u enough values but Im not great at medical so more help needed. thanks again guys u r life savers

could i also get help with this Question: i think they used √GM/r  instead √2GM/r

so does that mean its wrong or am I missing something? The answer is A

with the second one the Answer is D - i can't see how u would get there treating the speed of light as 3x10^8

another one - this i get why the answer is A - but shouldn't having the frequency mean you are decreasing the rate of change of magnetic flux? So it shouldn't just double EMF because the input is doubled - but stay the same since the rate was halved?

2 (Moon Question)

Escape velocity is calculated as



Subbing in the values given



So, the answer is B. If it says that the answer is A, it's just wrong.

17 (Photon)

For some stupidly annoying reason, we aren't given the wavelength. We need to actually count the wavelengths, and divide the given length by that. Literally the biggest waste of time.

By my count, there are 12 wavelengths in the diagram. So,



We can calculate frequency by





Cool, so the answer is either C or D, and the photon energy is



This is GREATER than the work function, so a photon is released. The answer is D.

9 (Cathode Ray)

Yes, the voltage should stay the same, and it does. The initial graph has a max at 200V. The final graph has a max at 200V. So, you're correct!

[jakesilove]

why/how do accelerating charges produce emr?
thanks  (background this is for quanta to quarks)

I didn't do Quanta, but I SUSPECT this is something you should just take on face value. It comes down to maths, relativity, and forces that I don't think you learn about. I don't want to write a confusing answer if it isn't needed, so I think I'll just leave it at that, but if someone who has done Quanta wants to jump in please do!

[beau77bro]

2 (Moon Question)

Escape velocity is calculated as



Subbing in the values given



So, the answer is B. If it says that the answer is A, it's just wrong.

17 (Photon)

For some stupidly annoying reason, we aren't given the wavelength. We need to actually count the wavelengths, and divide the given length by that. Literally the biggest waste of time.

By my count, there are 12 wavelengths in the diagram. So,



We can calculate frequency by





Cool, so the answer is either C or D, and the photon energy is



This is GREATER than the work function, so a photon is released. The answer is D.

9 (Cathode Ray)

Yes, the voltage should stay the same, and it does. The initial graph has a max at 200V. The final graph has a max at 200V. So, you're correct!

OK SWEET THANKYOU JAKE I APPRECIATE YOUR HELP SO MUCH also wth why is the second one so annoying? that's like just an unnessecary trick to see if ur paying attention - rude. thanks so much tho.

[Aaron12038488]

i have this assignment question on cosmic engine:
Describe 4 pieces of evidence which supports big bang theory
thx.