HSC Physics Question Thread

[austv99]

Would appreciate help with part ii for both pictures- the natural radioactivity one and the nuclear equation one
Thanks.

[justwannawish]

Hey guys, what exactly is g-force and when do you start experiencing it?
Also do astronauts in space actually experience gravity? My textbook says they are in freecall and thus experience acceleration due to gravity, but I don't get the correlation... sorry!

[bsdfjnlkasn]

Hey there!

I'm VERY confused about this question, what knowledge should I be applying here?
I know it's space, but that's about it!

[blasonduo]

Hey there!

I'm VERY confused about this question, what knowledge should I be applying here?
I know it's space, but that's about it!

Just for clarification, is it B?

If so, I'll be able to help! (if not oh no!)

[mary123987]

Hey guys, what exactly is g-force and when do you start experiencing it?
Also do astronauts in space actually experience gravity? My textbook says they are in freecall and thus experience acceleration due to gravity, but I don't get the correlation... sorry!

Hey in simple terms g- forces refers to a term used to express a person's apparent weight as a multiple of their true weight
that is g  forces = apparent weight /normal true weight
now apparent weight = mg +ma
and normal true weight = 9.8m (as w=mg where g = 9.8 )
now when subbing that in the m cancels and you are left with g + a /9.8
to answer your question g forces are first experienced during lift off or more appropriately it is apparent at this time why ? well when your on the earth accroding to the formula you should still experience a g-force of 1 (9.8+a/9.8 =1 as you are not accelerating whilst on the earth) why you dont experience though is because at this point F= W ( as f=mg and w=mg). so appropriately when f>w or f<w it is apparent .
whilst in space astronauts do experience gravity to a very small extent depending on the distance you are away from the radius of the earth the further away the smaller the value of g experienced .
Now an important thing to note is when in free fall a sense of weightlessness is experienced this is because the rocket is orbiting aound the earth horizontally and thus gforces = T/9.8m(now considering it is in free fall  T =0 as no fuel is being ejected and thus thrust =0) . If the rocket is falling its gravitational poential energy is inceasing and thus yes it is subject to downward acceleration due to gravity.
Hope this helps and makes sense if ur confused let me know

[justwannawish]

Hey in simple terms g- forces refers to a term used to express a person's apparent weight as a multiple of their true weight
that is g  forces = apparent weight /normal true weight
now apparent weight = mg +ma
and normal true weight = 9.8m (as w=mg where g = 9.8 )
now when subbing that in the m cancels and you are left with g + a /9.8
to answer your question g forces are first experienced during lift off or more appropriately it is apparent at this time why ? well when your on the earth accroding to the formula you should still experience a g-force of 1 (9.8+a/9.8 =1 as you are not accelerating whilst on the earth) why you dont experience though is because at this point F= W ( as f=mg and w=mg). so appropriately when f>w or f<w it is apparent .
whilst in space astronauts do experience gravity to a very small extent depending on the distance you are away from the radius of the earth the further away the smaller the value of g experienced .
Now an important thing to note is when in free fall a sense of weightlessness is experienced this is because the rocket is orbiting aound the earth horizontally and thus gforces = T/9.8m(now considering it is in free fall  T =0 as no fuel is being ejected and thus thrust =0) . If the rocket is falling its gravitational poential energy is inceasing and thus yes it is subject to downward acceleration due to gravity.
Hope this helps and makes sense if ur confused let me know

Yeah, it really did help
Just a follow up question, why does space not have gravity? Is it because it's a vacuum? Or is there gravity but it's very minute (if so, what type of gravity would it be)?

[mary123987]

Yeah, it really did help
Just a follow up question, why does space not have gravity? Is it because it's a vacuum? Or is there gravity but it's very minute (if so, what type of gravity would it be)?

That is ight there is most definitely gravity in space however it is so minute why?
well simply look at the law of universal gravitation where : F = Gm1m2/d
from this formula two things are very important
1) this gravity or attraction depends on distance
2) secind to that it depends on mass
for example consider the sun it is so huge (great mass) but consider how far it is , it is so far that this attreaction is almost 0 (you clearly dont see humans floating casually to the sun)
My point is gravity exists however it is incredibly minute , right now humans are attracted to anything : humans , particles anything but when compared to mass and distance attraction to the earth is greater .
hope that helps

[justwannawish]

That is ight there is most definitely gravity in space however it is so minute why?
well simply look at the law of universal gravitation where : F = Gm1m2/d
from this formula two things are very important
1) this gravity or attraction depends on distance
2) secind to that it depends on mass
for example consider the sun it is so huge (great mass) but consider how far it is , it is so far that this attreaction is almost 0 (you clearly dont see humans floating casually to the sun)
My point is gravity exists however it is incredibly minute , right now humans are attracted to anything : humans , particles anything but when compared to mass and distance attraction to the earth is greater .
hope that helps

Yep, that really did help thank you so much!!! It really helped me out

[mary123987]

Yep, that really did help thank you so much!!! It really helped me out

all good !!

[jamonwindeyer]

anyone know how galileo's analysis of projectile motion showed evidence to support his heliocentric model?

I don't think you'd be expected to answer this in a HSC exam, if it helps - And I've honestly got no clue how you'd link them!

Hey there!

I'm VERY confused about this question, what knowledge should I be applying here?
I know it's space, but that's about it!

So I'm pretty sure the logic is this. \(1.49\times10^{11}\) metres is the current distance and that gives a period of 1 year (we orbit the sun once a year, ish) and that gives a winter of 0.25 years. We need a winter of 10 years, meaning a 40x increase in the period, to 40 years.

By Kepler's Law of Periods, therefore:



Solving that should give B - So yep, you were on it blasonduo (increase the confidence my friend)

[raymatar]

Can someone explain this because I dont understand the solutions

Thanks

[winstondarmawan]

Quanta to Quarks:
Would appreciate help with this question, even after reading the solutions I am confused:
https://scontent-syd2-1.xx.fbcdn.net/v/t35.0-12/22070347_1853706338279156_1387821905_o.jpg?oh=0c3940feff466f0fe0c62a9317c8a023&oe=59CFE3C5
Solution: https://scontent-syd2-1.xx.fbcdn.net/v/t35.0-12/22095316_1853706898279100_1567201710_o.jpg?oh=55cabfc2a79f0599cc9cc6b5aa09370d&oe=59CFF432

[blasonduo]

Can someone explain this because I dont understand the solutions

Thanks

Hello! The question is asking how it is possible for a telescope to have the same orbital period than the Earth's.

From Kepler's laws of periods, it gives us a ratio as shown:



Given that this is a RATIO, when one variable changes, the other variable HAS to change to keep the equation true, which is shown in the question. We know that the telescope has a larger radius than Earth's so theoretically, it should have a LARGER period.

However, the question states that they both have the same orbital period, which contradicts Kepler's law, and this is because Kepler's law only applies to TWO objects, and doesn't take into account other forces.

For Earth, It has all of its force coming from the sun, HOWEVER, the telescope has forces from BOTH the sun AND the earth, meaning the telescope is experiencing more FORCE than Earth's. As force is equal to the centripetal force, it has a HIGHER orbital velocity.

Hope this helps

[itssona]

heey kinda confused about rockets :/ someone please check this?<br>
<br>
so basically, thrust force remains constant in the rocket, and because mass is decreasing due to fuels burning, acceleration increases. (due to f=ma). And due to increasinh acceleration, astronauts experience an increasing force (why??). And this increasing force is a g force.<br>
<br>
this means we need to decrease thrust (according to textbooks and ppl) ... but i dont get how thrust even relates to force on the ASTRONAUT. Plus, they say that this is why we should decrease thrust but first they say that thrust is constant.<br>
<br>
so lost, <br>
sorry and thank you all so much for the continuous help

[Zainbow]

heey kinda confused about rockets :/ someone please check this?<br>
<br>
so basically, thrust force remains constant in the rocket, and because mass is decreasing due to fuels burning, acceleration increases. (due to f=ma). And due to increasinh acceleration, astronauts experience an increasing force (why??). And this increasing force is a g force.<br>
<br>
this means we need to decrease thrust (according to textbooks and ppl) ... but i dont get how thrust even relates to force on the ASTRONAUT. Plus, they say that this is why we should decrease thrust but first they say that thrust is constant.<br>
<br>
so lost, <br>
sorry and thank you all so much for the continuous help

Hey! I'll try my best with explaining this one

Ok so, yes, the thrust force remains constant (in the first stage of rocket launch anyway) and due to the law of conservation of momentum the acceleration increases as mass decreases, which is what you've said. Due to 'a' increasing however, it is G-forces that increase and not the thrust force. So for this :

astronauts are experiencing an increasing force (why??)

, they're not really. Keep in mind that G's are not determined by force but by acceleration (hence the formula G = 1 + a/9.8 ).

I'm not really sure what you mean by decreasing thrust (hopefully someone else can explain this better), but basically, when the rocket nears the end of its first stage of launch and the first rockets run out of fuel, the thrust force pretty much disappears as the rockets stop firing and detach themselves. Here, because there is a momentary absence of thrust force, the acceleration drops dramatically and astronauts thus feel a momentary lack of G-forces, or weightlessness. This is until the second set of rockets fire up.