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December 09, 2021, 03:45:12 pm

### AuthorTopic: HSC Physics Question Thread  (Read 767853 times) Tweet Share

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#### nicholasbikolas

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##### Re: HSC Physics Question Thread
« Reply #3930 on: October 31, 2020, 12:05:24 pm »
+1
Can someone help me with this?

The total energy of a satellite is equal to the sum of its gravitational potential energy and its orbital kinetic energy. However, the work done to put that satellite into orbit is less than this.

Explain how this does not contravene the law of conservation of energy.

ok so basically our GPE is negative and approaching zero as we leave Earth. Our kinetic energy is positive and decreasing as we leave Earth. We have TWO components of energy when we are orbiting the Earth:
1) GPE of orbit
2) KE of orbiting

if we consider getting up into orbit, our kinetic energy (work done) converts into potential energy (our kinetic energy makes our GPE less negative). there is only the GPE component being established here.

so. to get up to orbit + ESTABLISH an orbit will cost much more energy than just to get up there??

hope this helps

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##### Re: HSC Physics Question Thread
« Reply #3931 on: October 31, 2020, 12:16:25 pm »
0
Can someone help me with this?

The total energy of a satellite is equal to the sum of its gravitational potential energy and its orbital kinetic energy. However, the work done to put that satellite into orbit is less than this.

Explain how this does not contravene the law of conservation of energy.

This was in our trials as well. I still don't properly understand it.

#### Coolmate

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##### Re: HSC Physics Question Thread
« Reply #3932 on: November 01, 2020, 11:12:10 pm »
0
Hi Everyone!

Could I please get some help with the following Module 8 questions:
🚀Question 1

🛰Question 2

☄Question 3

Coolmate
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#### fun_jirachi

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##### Re: HSC Physics Question Thread
« Reply #3933 on: November 02, 2020, 02:39:18 am »
+6
1. Recall that when a photon is absorbed, electrons 'jump' up energy levels. We can thus rule out B and D.
We can then use the formula $E= \frac{hc}{\lambda}$ to find the value of the energy change, which just so happens to be equivalent to the difference between levels 1 and 3 - hence, the answer is A.

2. Try to target these sorts of questions in the exam! The decay constant is equal to $\frac{\ln 2}{t_\frac{1}{2}}$. observe from the graph that the initial sample is 5g, so the half life is the time it takes to go down to 2.5g, which is about 29 years. Putting it into the calculator with that formula will get you an answer close to D.

3. Recall that when beta decay occurs, a neutron 'splits' into a proton and an electron (simplistically, kinda true). The electron is released (beta particle!) and the proton latches on to the nucleus. This means that there is one more proton and one less neutron. In heavier elements the ratio of protons to neutrons is about 1:1.5, so this will cause the ratio to go closer to 1:1 ie. towards the n=p line. Hence, the answer is A.
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]
Subject Acceleration (2018)
UCAT Question Compilation/FAQ (2020)

#### Coolmate

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##### Re: HSC Physics Question Thread
« Reply #3934 on: November 05, 2020, 03:08:00 pm »
0
1. Recall that when a photon is absorbed, electrons 'jump' up energy levels. We can thus rule out B and D.
We can then use the formula $E= \frac{hc}{\lambda}$ to find the value of the energy change, which just so happens to be equivalent to the difference between levels 1 and 3 - hence, the answer is A.

2. Try to target these sorts of questions in the exam! The decay constant is equal to $\frac{\ln 2}{t_\frac{1}{2}}$. observe from the graph that the initial sample is 5g, so the half life is the time it takes to go down to 2.5g, which is about 29 years. Putting it into the calculator with that formula will get you an answer close to D.

3. Recall that when beta decay occurs, a neutron 'splits' into a proton and an electron (simplistically, kinda true). The electron is released (beta particle!) and the proton latches on to the nucleus. This means that there is one more proton and one less neutron. In heavier elements the ratio of protons to neutrons is about 1:1.5, so this will cause the ratio to go closer to 1:1 ie. towards the n=p line. Hence, the answer is A.

Hey fun_jirachi!

Thankyou for your help!
I just had a question regarding Q3 --> Have I correctly solved the problem by doing this:
$\frac{\ln 2}{(29)\frac{1}{2}}$
= 0.04780325383
= 0.048

The final number wasn't any of the answers, but was closest to 'D'

Thanks again!
Coolmate
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#### fun_jirachi

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##### Re: HSC Physics Question Thread
« Reply #3935 on: November 05, 2020, 04:37:46 pm »
+3
Hey there Coolmate

Remember that the subscripted half actually means half-life (the half denotes half-life as opposed to regular t) - it does not mean multiply the denominator by half (which is what I assume you did, considering that your answer is roughly twice the size of D). Just be careful with these sorts of things - if an answer doesn't look right, it probably isn't! In general, look for an error percentage that seems reasonable if interpreting from a graph or some other data set, or an exact result if you're given actual numbers. Otherwise, the method seems okay
« Last Edit: November 05, 2020, 06:47:08 pm by fun_jirachi »
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]
Subject Acceleration (2018)
UCAT Question Compilation/FAQ (2020)

#### Coolmate

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##### Re: HSC Physics Question Thread
« Reply #3936 on: November 05, 2020, 05:57:42 pm »
0
Hey there Coolmate

Remember that the subscripted half actually means half-life (the half denotes half-life as opposed to regular t) - it does not mean multiply the denominator by half (which is what I assume you did, consider that your answer is roughly twice the size of D). Just be careful with these sorts of things - if an answer doesn't look right, it probably isn't! In general, look for an error percentage that seems reasonable if interpreting from a graph or some other data set, or an exact result if you're given actual numbers. Otherwise, the method seems okay

Ohhh, ok I see that now

When doing just ln(2)/(29), I got an answer of 0.024, which is the closest one. This makes sense now, thanks again for your help

Coolmate
🤯HSC 2020:🤯
🔥Advanced Maths🔥 - 📚Advanced English📚 - ☄️Physics☄️ - ✌Biology✌ - 🙏SOR 1🙏 - 👨‍💻IPT👨‍💻

🎓University 2021 - 2025:
Bachelor of Science (Biology) / Bachelor of Information Technology (Cyber Security)

🧬Biology Guide:
🧪Module 5

#### Maroon and Gold Never Fold

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##### Re: HSC Physics Question Thread
« Reply #3937 on: August 07, 2021, 08:29:21 pm »
0
Explain, in your own words, at least 3 different stages of evolution that
the universe underwent as described by the Big Bang theory. (4 marks)

I wasn't sure about this question as there are no answers. My answer included: 1. initial bang (release of energy) 2. inflation (universe cool with pair production) and 3. production of elements (lithium, hydrogen and helium). Not sure if this is right or I have missed anything.

#### crippledbyenglish

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##### Re: HSC Physics Question Thread
« Reply #3938 on: November 18, 2021, 04:54:08 pm »
0
#1
Hi! I have been doing a few practice papers for physics and have a bunch of questions I am confused about! Does anyone know:

1. What is the best definition for an uncontrolled/controlled chain reaction. I would have said the number of fissions subsequently initiated in comparison to the number of original fissions but have also see it defined in terms of rate.
2. Why can't a particle in free fall move straight past Earth? What if gravity was pulling in two opposing directions and these cancelled out?
3. How does precision work for experiments and stuff I can find a standard answer literally nowhere
4. In back emf graphs why is back emf proportional to motor speed if emf changes periodically as the rotor rotates

If you could explain it would be greatly appreciated!