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March 29, 2024, 04:57:07 am

Author Topic: HSC Physics Marathon[NEW SYLLABUS]  (Read 17856 times)  Share 

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THSCStudyOnly

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Re: Weekly HSC Physics Marathon[NEW SYLLABUS]
« Reply #15 on: October 03, 2019, 10:38:16 pm »
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Question 3:

This is a good question. You will need to think!

A very good question for the new syllabus!

Let me add just in case, you may make the assumption that the effect of gravity on the electron is negligible

Also typo. The time spent between the plates should be 2.6 times 10^{-9} in the 2nd last line!

Is it 0.10699m = 10.7cm? I'll give working if it's correct (tbh i'm not sure, I am bound to make a silly mistake somewhere even if I have the process right)

fun_jirachi

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Re: Weekly HSC Physics Marathon[NEW SYLLABUS]
« Reply #16 on: October 04, 2019, 11:11:51 am »
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Question 3:
-snip-
Is it 0.10699m = 10.7cm? I'll give working if it's correct (tbh i'm not sure, I am bound to make a silly mistake somewhere even if I have the process right)

Thanks for bumping this thread, was going to answer Q2 but totally forgot about all it! Now there's a Q3 as well :)

I got a different answer for Q3, but will likewise post if I'm correct? I'm not too sure of myself because of the wordiness of the question, spent quite a bit of time just trying to understand what the question was asking :)

My answer
7.2cm
Spoiler
HSC 2018: Mod Hist [88] | 2U Maths [98]
HSC 2019: Physics [92] | Chemistry [93] | English Adv [87] | 3U Maths [98] | 4U Maths [97]
ATAR: 99.05

UCAT: 3310 - VR [740] | DM [890] | QR [880] | AR [800]
Guide Links:
Subject Acceleration (2018)
UCAT Question Compilation/FAQ (2020)
Asking good questions

THSCStudyOnly

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Re: Weekly HSC Physics Marathon[NEW SYLLABUS]
« Reply #17 on: October 04, 2019, 11:15:34 am »
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Ye, I had a tough time visualising it hence why I am not sure it is correct. Hoping they give diagrams in the actual HSC.

DrDusk

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Re: Weekly HSC Physics Marathon[NEW SYLLABUS]
« Reply #18 on: October 04, 2019, 04:06:04 pm »
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Thanks for bumping this thread, was going to answer Q2 but totally forgot about all it! Now there's a Q3 as well :)

I got a different answer for Q3, but will likewise post if I'm correct? I'm not too sure of myself because of the wordiness of the question, spent quite a bit of time just trying to understand what the question was asking :)

My answer
7.2cm

Well done!

This is correct

DrDusk

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Re: Weekly HSC Physics Marathon[NEW SYLLABUS]
« Reply #19 on: October 04, 2019, 04:07:26 pm »
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Is it 0.10699m = 10.7cm? I'll give working if it's correct (tbh i'm not sure, I am bound to make a silly mistake somewhere even if I have the process right)

Could you please post your working out so I can have a look at it

DrDusk

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Re: Weekly HSC Physics Marathon[NEW SYLLABUS]
« Reply #20 on: October 04, 2019, 04:56:28 pm »
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Question 3 answer.

They wont always provide a diagram. Sometimes there really is a lot of info so you gotta learn to stay calm and work your way through it.

A question like this can definitely appear in a trial or hsc exam.

fun_jirachi

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Re: Weekly HSC Physics Marathon[NEW SYLLABUS]
« Reply #21 on: October 04, 2019, 05:04:52 pm »
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Question 3 answer.

They wont always provide a diagram. Sometimes there really is a lot of info so you gotta learn to stay calm and work your way through it.

A question like this can definitely appear in a trial or hsc exam.

Yeah, that's what I did. I think a lot of the big words got me confused, and it took me a while to realise what the question was actually asking :) Thanks for the question though, definitely challenging! Hope there's more to come :)
Spoiler
HSC 2018: Mod Hist [88] | 2U Maths [98]
HSC 2019: Physics [92] | Chemistry [93] | English Adv [87] | 3U Maths [98] | 4U Maths [97]
ATAR: 99.05

UCAT: 3310 - VR [740] | DM [890] | QR [880] | AR [800]
Guide Links:
Subject Acceleration (2018)
UCAT Question Compilation/FAQ (2020)
Asking good questions

THSCStudyOnly

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Re: Weekly HSC Physics Marathon[NEW SYLLABUS]
« Reply #22 on: October 04, 2019, 05:09:52 pm »
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Well done for getting it!
I redid it a different way and still got it wrong because I used negative acceleration....
I used qE=ma and solved for acceleration in the first plate (after using V=Ed to find E) then I used it to find the v (using kinematic equations) coming into the second set of plates. After this I found the acceleration in the second set of plates (using same thing I did for the above ones). Then I used s=ut+1/2at^2 to plug those values in, but I used negative acceleration (because a=qE/m gave me a negative value which I forgot to times by negative again because the electron in moving down). My bad.
« Last Edit: October 04, 2019, 05:12:12 pm by THSCStudyOnly »

DrDusk

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Re: Weekly HSC Physics Marathon[NEW SYLLABUS]
« Reply #23 on: October 04, 2019, 05:25:47 pm »
+2
Well done for getting it!
I redid it a different way and still got it wrong because I used negative acceleration....
I used qE=ma and solved for acceleration in the first plate (after using V=Ed to find E) then I used it to find the v (using kinematic equations) coming into the second set of plates. After this I found the acceleration in the second set of plates (using same thing I did for the above ones). Then I used s=ut+1/2at^2 to plug those values in, but I used negative acceleration (because a=qE/m gave me a negative value which I forgot to times by negative again because the electron in moving down). My bad.
That's really great as well. You would still get 2/3 for it so good job!

I hope this teaches you to always picture the scenario in your head when dealing with situations like this. I would recommend drawing the diagram and labeling the vectors for acceleration. This will reduce the chance of you making that silly mistake again

THSCStudyOnly

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Re: Weekly HSC Physics Marathon[NEW SYLLABUS]
« Reply #24 on: October 04, 2019, 05:29:47 pm »
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Ye, lesson learn't. The wordiness of the question gets to me (especially in an exam setting). I got to read the question again and again until I completely understand it.

DrDusk

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Re: Weekly HSC Physics Marathon[NEW SYLLABUS]
« Reply #25 on: October 13, 2019, 04:20:20 pm »
+1
Question 4:
This is definitely a kind of question you can be asked because the Math itself is simple but requires you to make an observation that may be difficult to spot =)

Definitely more of a challenging uniform circular motion/Magnetism question!
« Last Edit: October 13, 2019, 04:24:07 pm by DrDusk »

fun_jirachi

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Re: HSC Physics Marathon[NEW SYLLABUS]
« Reply #26 on: October 13, 2019, 07:19:10 pm »
+1
My answers
Hope these are right! :)
i) Into the page. (Used left-hand grip rule)
ii)


Spoiler
HSC 2018: Mod Hist [88] | 2U Maths [98]
HSC 2019: Physics [92] | Chemistry [93] | English Adv [87] | 3U Maths [98] | 4U Maths [97]
ATAR: 99.05

UCAT: 3310 - VR [740] | DM [890] | QR [880] | AR [800]
Guide Links:
Subject Acceleration (2018)
UCAT Question Compilation/FAQ (2020)
Asking good questions

DrDusk

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Re: HSC Physics Marathon[NEW SYLLABUS]
« Reply #27 on: October 13, 2019, 07:22:07 pm »
+2
My answers
Hope these are right! :)
i) Into the page. (Used left-hand grip rule)
ii)


Wowie well done! Your smashing them. However you may want to re-consider your part (i)  ;)

frog0101

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Re: Weekly HSC Physics Marathon[NEW SYLLABUS]
« Reply #28 on: October 21, 2019, 05:22:45 pm »
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Question 3 answer.

They wont always provide a diagram. Sometimes there really is a lot of info so you gotta learn to stay calm and work your way through it.

A question like this can definitely appear in a trial or hsc exam.

I thought that since the electron is being accelerated horizontally by the electron gun,
Not sure that the way I am visualising this is correct (horizontal acceleration and then vertical acceleration), but wouldn't only the horizontal parallel plates accelerate the electron in the vertical direction?
Thanks

THSCStudyOnly

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Re: HSC Physics Marathon[NEW SYLLABUS]
« Reply #29 on: October 26, 2019, 08:19:16 pm »
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My solution, I think it may be easier to see, but bit longer to do :P ;D
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i) Out of page (using rhpr but flipped hand because electrons)

ii) Using mass spectomrtry equation
i.e. qvB=mv2/r
r = mv/qB
rearranging v = rqB/m .............. (1)

Now Consider:
K = (1/2)mv2
rearrange to make v subject: v = sqrt(2K/m) ............... (2)

Equating (1) and (2)
sqrt(2K/m) = rqB/m
2K/m = (r2q2B2)/m2
Just rearrange to make B2 subject
B2 > 2Km/q2r2
B > sqrt((2Km/q2r2))
(Now: q=e and r=d)
B > sqrt((2Km/e2d2))
There may be lots of errors because it is too messy to read with this crap formatting.

« Last Edit: October 26, 2019, 09:57:26 pm by THSCStudyOnly »