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March 28, 2024, 09:23:24 pm

Author Topic: HSC Physics Question Thread  (Read 1030402 times)  Share 

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jamonwindeyer

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Re: HSC Physics Question Thread
« Reply #3720 on: May 13, 2019, 12:10:59 pm »
+6
I understand proton-proton chain reactions and I know about them, but I don't understand how to do this question.

Cool! So in that case, you know that the P-P chain reactions turn four protons (Hydrogen nuclei) into a helium nucleus (two protons, two neutrons). To do this question properly you need to know the mass of a helium nucleus, which isn't given in the question, you might have it in a supplementary data sheet?

In any case, you calculate the difference in the masses between the Helium and the four protons - That gives you what we call the mass defect. We'll call this \(\Delta m\). Then calculate the energy released via:



Now, we're given the luminosity of the star in Watts. Remember that this is joules per second - Let's figure out how many reactions we need:



So we have this many reactions per second, which means we convert \(4m_p\) kilograms of protons into helium per second, where \(m_p\) is the mass of the proton. Mass per year is obtained by progressively multiplying to get mass per minute, hour, days and year!



Final question is just figuring out, with this rate of mass being converted per year, how long will it take to burn certain amounts of hydrogen. Remember the total start hydrogen mass is \(0.75\times1.99\times10^{30}=1.4925\times10^{30}\) kilograms, 75% of the mass of the sun! So figure out 12% of this and then determine how long that takes based on your answer to (b)! :)

Hopefully this outline is helpful! Let me know if you get stuck anywhere as you follow ;D

david.wang28

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Re: HSC Physics Question Thread
« Reply #3721 on: May 13, 2019, 08:14:24 pm »
+1
Cool! So in that case, you know that the P-P chain reactions turn four protons (Hydrogen nuclei) into a helium nucleus (two protons, two neutrons). To do this question properly you need to know the mass of a helium nucleus, which isn't given in the question, you might have it in a supplementary data sheet?

In any case, you calculate the difference in the masses between the Helium and the four protons - That gives you what we call the mass defect. We'll call this \(\Delta m\). Then calculate the energy released via:



Now, we're given the luminosity of the star in Watts. Remember that this is joules per second - Let's figure out how many reactions we need:



So we have this many reactions per second, which means we convert \(4m_p\) kilograms of protons into helium per second, where \(m_p\) is the mass of the proton. Mass per year is obtained by progressively multiplying to get mass per minute, hour, days and year!



Final question is just figuring out, with this rate of mass being converted per year, how long will it take to burn certain amounts of hydrogen. Remember the total start hydrogen mass is \(0.75\times1.99\times10^{30}=1.4925\times10^{30}\) kilograms, 75% of the mass of the sun! So figure out 12% of this and then determine how long that takes based on your answer to (b)! :)

Hopefully this outline is helpful! Let me know if you get stuck anywhere as you follow ;D
Thank you Jamon! :)
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Joseph.Ryan

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Re: HSC Physics Question Thread
« Reply #3722 on: May 17, 2019, 01:35:54 pm »
0
Hi, do we need to know how to derive the Lorenz transformations equations for the hsc exam?

DrDusk

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Re: HSC Physics Question Thread
« Reply #3723 on: May 17, 2019, 06:53:26 pm »
0
Hi, do we need to know how to derive the Lorenz transformations equations for the hsc exam?
I love your enthusiasm but no :)
It's not that hard imo so don't let that stop you from trying :P
If your teacher actually knows his/hers Physics, they might even do it for you
« Last Edit: May 17, 2019, 06:56:16 pm by DrDusk »

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Re: HSC Physics Question Thread
« Reply #3724 on: May 19, 2019, 09:32:39 pm »
0
Can someone please explain this to me: "The interference occurs because the waves have travelled a different distance from each slit to the surface, depending on which point you are looking at on the surface." (It's from the "Young's double slit experiment" section in the Course Notes books).


DrDusk

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Re: HSC Physics Question Thread
« Reply #3725 on: May 19, 2019, 10:05:28 pm »
+2
Can someone please explain this to me: "The interference occurs because the waves have travelled a different distance from each slit to the surface, depending on which point you are looking at on the surface." (It's from the "Young's double slit experiment" section in the Course Notes books).

Well if you draw a line from each slit to any arbitrary point on the surface, the lines will be of different length. Thus each wave has traveled a different distance to reach that point. As a result of this when the waves collide they will be slightly offset from each other, causing them to interfere. Depending on how much they are offset by they will either constructively or destructively interfere.

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Re: HSC Physics Question Thread
« Reply #3726 on: May 26, 2019, 10:18:09 pm »
0
Hi everyone,

I'm in year 11 and I have come across these questions (questions attached below) and I am confused about how to go about answering it, would someone please be able to help me here!

Cheers :)
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fun_jirachi

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Re: HSC Physics Question Thread
« Reply #3727 on: May 26, 2019, 11:03:05 pm »
+4
Hey there!

Gonna try guiding you instead of giving the answers to you straight up, since you need to going through these thought processes in an exam :)

6. a) Try using the equation W=Fs using the information given!
b) Remember that the work done is equal to the change in energy (this isn't technically correct in the real world, but it's a simplification we're using).
c) Equate the value from a) using E=0.5mv^2
d) Self explanatory, it's given in the question :)
e) Given acceleration, displacement, and initial velocity, try using one of the kinematic equations (SUVAT) to relate these three quantities to time!

7. a) Given that KE=0.5mv^2, calculate the initial and final kinetic energy and find the difference :)
b) Equate this value to work done to find the force acting over a distance that slows it down (W=Fs)
c) It's basically just a frictional force acting against the tires in the opposite direction to motion :)
d) similar to d) and e) from above :)

If you need any further help/full working, glad to provide it :) Hope this helps!
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Coolmate

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Re: HSC Physics Question Thread
« Reply #3728 on: May 28, 2019, 10:09:52 am »
0
Hey there!

Gonna try guiding you instead of giving the answers to you straight up, since you need to going through these thought processes in an exam :)

6. a) Try using the equation W=Fs using the information given!
b) Remember that the work done is equal to the change in energy (this isn't technically correct in the real world, but it's a simplification we're using).
c) Equate the value from a) using E=0.5mv^2
d) Self explanatory, it's given in the question :)
e) Given acceleration, displacement, and initial velocity, try using one of the kinematic equations (SUVAT) to relate these three quantities to time!

7. a) Given that KE=0.5mv^2, calculate the initial and final kinetic energy and find the difference :)
b) Equate this value to work done to find the force acting over a distance that slows it down (W=Fs)
c) It's basically just a frictional force acting against the tires in the opposite direction to motion :)
d) similar to d) and e) from above :)

If you need any further help/full working, glad to provide it :) Hope this helps!

Thanks fun_jirachi

I understand it now!  ;D
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david.wang28

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Re: HSC Physics Question Thread
« Reply #3729 on: May 29, 2019, 09:58:45 pm »
0
Hello,
I am stuck on a projectile motion question. I've posted my working out, and I don't quite know how to do all of the question. Can anyone please help me out? Thanks :)
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david.wang28

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Re: HSC Physics Question Thread
« Reply #3730 on: May 29, 2019, 10:02:41 pm »
0
Hello,
I have another question on projectile motion. This time, I don't know how to figure out the angle in the last part of the question. Can anyone please help me out? Thanks :)
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DrDusk

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Re: HSC Physics Question Thread
« Reply #3731 on: May 29, 2019, 11:15:36 pm »
+2
Hello,
I am stuck on a projectile motion question. I've posted my working out, and I don't quite know how to do all of the question. Can anyone please help me out? Thanks :)
a)
Remember the horizontal velocity of the projectile does not change, and at the peak the y component of velocity will be zero. So the net velocity at the peak is just the initial horizontal velocity..

b) Your working seems fine..

c) We want the time of flight to be 3 seconds. To make things easier we should instead think of it as it should take 1.5 seconds to reach its peak.





« Last Edit: May 30, 2019, 02:15:26 am by DrDusk »

DrDusk

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Re: HSC Physics Question Thread
« Reply #3732 on: May 29, 2019, 11:35:33 pm »
+2
Hello,
I have another question on projectile motion. This time, I don't know how to figure out the angle in the last part of the question. Can anyone please help me out? Thanks :)
For this part you must remember that the horizontal and vertical motions are separate from each other.
Now lets look at the energies. The horizontal velocity is always constant which means the horizontal component of kinetic energy is also constant. This means we can say that all the initial vertical kinetic energy is converted to potential energy at its peak, because remember at the peak the vertical component of velocity is zero.



Just a piece of advice...It is a very important skill in physics that you are always thinking creatively and methodically. In your mind you should always constantly be going through any laws such as conservation of energy, momentum etc. Brainstorm all the rules that can apply.
Also because this is HSC Physics almost all of the time the so called 'hard' calculation problems boil down to just equating two formulas...
So basically if you absolutely have no idea what to do, just think of two formulas that apply really well and equate them as a last resort.
« Last Edit: June 21, 2019, 05:04:34 pm by DrDusk »

david.wang28

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Re: HSC Physics Question Thread
« Reply #3733 on: May 30, 2019, 09:06:32 am »
0
Great advice DrDusk! Also, thanks for the help :)
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Coolmate

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Re: HSC Physics Question Thread
« Reply #3734 on: June 03, 2019, 06:53:47 pm »
0
Hello!
Would someone please be able to explain to me the common misconception, gravity is a force of attraction between 2 objects with mass. Including the General Theory of Relativity? and any advice about depth studies and how to get good marks?
Thanks :)
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