July 10, 2020, 09:19:11 am

### AuthorTopic: HSC Physics Marathon[NEW SYLLABUS]  (Read 4670 times) Tweet Share

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#### DrDusk

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##### Re: HSC Physics Marathon[NEW SYLLABUS]
« Reply #30 on: October 26, 2019, 09:42:37 pm »
+2
My solution, I think it may be easier to see, but bit longer to do
Spoiler
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/qr
B > sqrt((2Km/qr))
(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.
Well done on this attempt!

$\text{Just a few points I must make. You went from }$
$\dfrac{2K}{m} = \dfrac{r^2q^2B^2}{m^2}\hspace{2mm}\text{to} \\ B^2 \geq \dfrac{2Km}{qr} \\ \text{However you have not justified from going = to >} \\ \text{And also I think the qr should be}\hspace{2mm}q^2r^2 \\ \text{Your definitely on the right track but your just missing one observation that allows you to justify the change from = to >} \\ \text{Draw a picture of the electrons path and think about what must happen if its circular path does not intsersect the plate}$

Well done on getting this far! You've almost got it
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#### DrDusk

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##### Re: HSC Physics Marathon[NEW SYLLABUS]
« Reply #31 on: November 27, 2019, 09:55:39 pm »
+5
UPDATE:
Now that the HSC has happened we know what level of questions to expect.
With my finals finishing in the next 2/3 weeks. I will be releasing a whole papers worth of questions!

Coincidentally a question that appeared in the HSC was one of the questions that I uploaded here!
« Last Edit: November 27, 2019, 09:59:18 pm by DrDusk »
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#### Coolmate

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##### Re: HSC Physics Marathon[NEW SYLLABUS]
« Reply #32 on: November 27, 2019, 10:55:58 pm »
+1
UPDATE:
Now that the HSC has happened we know what level of questions to expect.
With my finals finishing in the next 2/3 weeks. I will be releasing a whole papers worth of questions!

Coincidentally a question that appeared in the HSC was one of the questions that I uploaded here!

Thanks DrDusk!
This is very exciting, I can't wait to complete some questions!

Coolmate
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#### mani.s_

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##### Re: Weekly HSC Physics Marathon
« Reply #33 on: December 04, 2019, 10:30:22 pm »
0
Question 1:

This one is quite easy. Make sure to set your working and equations out clearly.
What does it mean by far the ball has dropped when it strikes the hill???

#### DrDusk

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##### Re: Weekly HSC Physics Marathon
« Reply #34 on: December 04, 2019, 10:32:34 pm »
+1
What does it mean by far the ball has dropped when it strikes the hill???
It means what is it's 'y' displacement from where it was launched.
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#### mani.s_

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##### Re: Weekly HSC Physics Marathon
« Reply #35 on: December 04, 2019, 10:34:30 pm »
0
It means what is it's 'y' displacement from where it was launched.
So its height at the marked point? or are you talking about its range for the launch position?
« Last Edit: December 04, 2019, 10:36:47 pm by mani.s_ »

#### DrDusk

• NSW MVP - 2019
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##### Re: Weekly HSC Physics Marathon
« Reply #36 on: December 04, 2019, 10:39:30 pm »
+1
So its height at the marked point? or are you talking about its range for the launch position?
It's how far it as fallen so (the height of the building) - (it's height at that point)
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#### mani.s_

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##### Re: Weekly HSC Physics Marathon
« Reply #37 on: December 04, 2019, 10:42:01 pm »
0
It's how far it as fallen so (the height of the building) - (it's height at that point)
ohhhh ok. Thank you so much!!!

#### mani.s_

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##### Re: Weekly HSC Physics Marathon[NEW SYLLABUS]
« Reply #38 on: February 25, 2020, 10:06:10 am »
0
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!
Hi, for this question I was wondering why $u_y$ won't be 0. The electron gun causes the electron to have a initial velocity but isn't that velocity in the horizontal direction? So the initial velocity in the y direction be 0?