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#### shekhar.patel

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##### Re: HSC Physics Question Thread
« Reply #3855 on: January 04, 2020, 04:06:04 pm »
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A catapult launches a 2.0 kg rock at 3.2 m/s, 30° elevation, from a 7.0 m high rooftop determine the total horizontal displacement.
I am getting answer as 0.9m. But it is wrong, I am not quite sure why.

#### DrDusk

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##### Re: HSC Physics Question Thread
« Reply #3856 on: January 05, 2020, 02:39:50 pm »
+2
A catapult launches a 2.0 kg rock at 3.2 m/s, 30° elevation, from a 7.0 m high rooftop determine the total horizontal displacement.
I am getting answer as 0.9m. But it is wrong, I am not quite sure why.
Do you mind showing your working out? Usually especially for projectile motion it's just a small error such as a negative sign being somewhere it shouldn't.
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#### mani.s_

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##### Re: HSC Physics Question Thread
« Reply #3857 on: January 06, 2020, 06:21:29 pm »
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A catapult launches a 2.0 kg rock at 3.2 m/s, 30° elevation, from a 7.0 m high rooftop determine the total horizontal displacement.
I am getting answer as 0.9m. But it is wrong, I am not quite sure why.
I'm getting 10.13m, is that correct?

#### blasonduo

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##### Re: HSC Physics Question Thread
« Reply #3858 on: January 06, 2020, 07:50:26 pm »
+6
I'm getting 10.13m, is that correct?

Hey! By doing this question, I get a value of 3.80 meters. So something has gone wrong with the answers and your working!

An easy, intuitive way to see if you're on the right track is to visualise it. 0.9m seems way too small for the height of the cliff (this would correlate with a time of flight of about 0.32 seconds!), but 10.13m seems too big for the speed the rock (time of flight for this would be around 3.66 seconds, dropping the rock from the height of 7 meters would be around 1.2 seconds, so adding another 2.4 seconds seems a bit too much for the speed of the rock)

If you'd want to post your working, I might be able to see where you went wrong!
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#### Coolmate

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##### Re: HSC Physics Question Thread
« Reply #3859 on: January 07, 2020, 01:10:12 pm »
0
Hey Coolmate,

It really depends on the parameters of your depth study and the associated marking criteria but everything you've mentioned certainly differentiates a Band 5 from a Band 6. Here are a couple more pointers:

- If you need to assess the validity + accuracy + reliability of the primary/secondary investigation, you really need to know the difference between these terms, and not just acknowledge them under one 'umbrella'. Critically evaluate all aspects of your depth study.
- Clearly established inquiry question and a valid investigation (primary OR secondary) that addresses this question. Conclusion made that clearly reflects your findings.
- As you mentioned, include all appropriate Physics formulae. Perhaps derive such formulae if it is relevant to your depth study (e.g. if it is investigating circular motion)
- Your depth study should also be well-structured and clear.
- Research should indeed be in-depth, as you've pointed out, but try not to digress from the question at hand.

This list isn't exhaustive, but should point you in the right direction I'd highly recommend reading your marking criteria if you have access to it and pay attention to the modality used in each mark bracket (e.g. a Band 5 might be "thorough" but a Band 6 might be "extensive")

Hope I could be of some assistance!

Thanks louisaaa01 for your in-depth response! It is really helping me as I am doing my depth study!

Thanks again, Coolmate
« Last Edit: January 07, 2020, 07:08:43 pm by Coolmate »
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#### Coolmate

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##### Re: HSC Physics Question Thread
« Reply #3860 on: January 07, 2020, 07:14:59 pm »
0
Hi everyone!

I am a bit confused about the questions below, that are in my depth study and what kind of specific information would be required for each of these questions. If anyone could please provide any helpful tips, that will be much appreciated:

1)   Keeping Low Earth Satellites in Orbit
Use Physics principles to explain how Low Earth Satellites are able to travel in circular motion to orbit the Earth at a uniform speed and how and why these orbits are maintained.

2)   Explaining weightlessness
For manned space satellites, discuss why astronauts live in conditions of ‘apparent’ weightlessness.

Coolmate
🤯HSC 2020 (21 Days):🤯

🔥Advanced Maths🔥 - 📚Advanced English📚 - ☄️Physics☄️ - ✌Biology✌ - 🙏SOR 1🙏 - 👨‍💻IPT👨‍💻

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#### mani.s_

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##### Re: HSC Physics Question Thread
« Reply #3861 on: January 07, 2020, 08:16:55 pm »
+1
Hey! By doing this question, I get a value of 3.80 meters. So something has gone wrong with the answers and your working!

An easy, intuitive way to see if you're on the right track is to visualise it. 0.9m seems way too small for the height of the cliff (this would correlate with a time of flight of about 0.32 seconds!), but 10.13m seems too big for the speed the rock (time of flight for this would be around 3.66 seconds, dropping the rock from the height of 7 meters would be around 1.2 seconds, so adding another 2.4 seconds seems a bit too much for the speed of the rock)

If you'd want to post your working, I might be able to see where you went wrong!
hmmm I just did the question again and I also got 3.7955m which rounds to 3.8m. I don't know how I did it incorrectly the first time. I think for the speed, I took 32m/s instead of 3.2 when calculating the time using S=ut + 1/2at^2. Thank you so much for spotting my error and correcting it

#### blasonduo

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##### Re: HSC Physics Question Thread
« Reply #3862 on: January 07, 2020, 08:30:47 pm »
+4
Hi everyone!

I am a bit confused about the questions below, that are in my depth study and what kind of specific information would be required for each of these questions. If anyone could please provide any helpful tips, that will be much appreciated:

1)   Keeping Low Earth Satellites in Orbit
Use Physics principles to explain how Low Earth Satellites are able to travel in circular motion to orbit the Earth at a uniform speed and how and why these orbits are maintained.

2)   Explaining weightlessness
For manned space satellites, discuss why astronauts live in conditions of ‘apparent’ weightlessness.

Coolmate

Hey! I'd hate to be that person, but I genuinely believe for questions like these, it's best for your learning if you give it a shot and try your best at explaining it. From there, I'll happily see if you need anything added.

Again, if I just told you what needs to be included, the chances of it sticking (the things you omitted of course) are much lower. I look forward to seeing what you come up with!
2018: UNSW B science (physics)/B education

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#### mani.s_

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##### Re: HSC Physics Question Thread
« Reply #3863 on: January 08, 2020, 03:50:03 pm »
0
Hi, for projectile motion in uniform electric fields, do we define theta perpendicular to the field or parallel to the field??? Which one should we use for theta when we want to break down the velocity vector into its components (parallel and perpendicular)

Physics In Focus says to define it parallel to the field as shown in the first image that I have attached, but I'm not sure why.

#### DrDusk

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##### Re: HSC Physics Question Thread
« Reply #3864 on: January 08, 2020, 04:22:22 pm »
+2
Hi, for projectile motion in uniform electric fields, do we define theta perpendicular to the field or parallel to the field??? Which one should we use for theta when we want to break down the velocity vector into its components (parallel and perpendicular)

Physics In Focus says to define it parallel to the field as shown in the first image that I have attached, but I'm not sure why.
They're the exact same thing, like actually the exact same thing. Do it how you always do it.
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#### shekhar.patel

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##### Re: HSC Physics Question Thread
« Reply #3865 on: January 14, 2020, 09:32:15 pm »
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Hi, for the following question I am confused why the answers are as such. Any help would be great. Thanks.

#### insanipi

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##### Re: HSC Physics Question Thread
« Reply #3866 on: January 14, 2020, 09:47:29 pm »
+6
Hi, for the following question I am confused why the answers are as such. Any help would be great. Thanks.
With current, we follow the right-hand grip rule (thumb in direction of current, fingers going out are the dots, and fingernails coming towards your thumb is the crosses going in).

With electron flow, this is the reverse. There are two ways to do this:
- left hand rule (exactly like the right-hand grip rule)
- or, the opposite directions as to the right hand rule suggests!

Hope this helps!
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#### shekhar.patel

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##### Re: HSC Physics Question Thread
« Reply #3867 on: January 14, 2020, 09:56:32 pm »
+1
With current, we follow the right-hand grip rule (thumb in direction of current, fingers going out are the dots, and fingernails coming towards your thumb is the crosses going in).

With electron flow, this is the reverse. There are two ways to do this:
- left hand rule (exactly like the right-hand grip rule)
- or, the opposite directions as to the right hand rule suggests!

Hope this helps!

Thanks a lot. I understand it now.

#### shekhar.patel

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##### Re: HSC Physics Question Thread
« Reply #3868 on: January 15, 2020, 10:14:37 pm »
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Hi, In this questions is I am confused about the angle that theta should be.

#### blasonduo

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##### Re: HSC Physics Question Thread
« Reply #3869 on: January 16, 2020, 12:20:47 am »
+6
Hi, In this questions is I am confused about the angle that theta should be.

Hey!

The first thing you should note is that if we rotate this wire such that it is vertical, nothing here changed, the magnetic field still passes directly through the wire, meaning on this axis, the angle in which it is held does not matter, so the value for sine is 90. (because the angle that the rod and the magnetic field makes will always be 90, no matter which way we orientate our wire on this axis we spoke about earlier)

Hope this helps!
« Last Edit: January 16, 2020, 12:25:27 am by blasonduo »
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