HSC Physics Predictions / Thoughts (1 Viewer)

[JeydinNewWon]

For question 20, there has been disputes over where it is A) or D). But I think I have a definitive case for why it is, in fact, A. When the ball undergoes a projectile-ish motion with the semi-circular ramp, it has both horizontal and vertical velocity components, right?

However! the centripetal force has a velocity component that is PERPENDICULAR to it. Considering the centripetal force is the Normal, this means the horizontal velocity component of the "projectile path" must be the velocity in the centripetal force, hence the centripetal force must be constant.

Also, remember, the centripetal force cannot have a velocity that is not constant--I don't think that makes sense.

So I'm a bit confused as to why MATRIX has set Q20 as D).

 

[NN03]

For question 20, there has been disputes over where it is A) or D). But I think I have a definitive case for why it is, in fact, A. When the ball undergoes a projectile-ish motion with the semi-circular ramp, it has both horizontal and vertical velocity components, right?

However! the centripetal force has a velocity component that is PERPENDICULAR to it. Considering the centripetal force is the Normal, this means the horizontal velocity component of the "projectile path" must be the velocity in the centripetal force, hence the centripetal force must be constant.

Also, remember, the centripetal force cannot have a velocity that is not constant--I don't think that makes sense.

So I'm a bit confused as to why MATRIX has set Q20 as D).

I legit got a lucky guess and put A as the answer. God was with me on that one.

 

[wizzkids]

2020 HSC Physics
MC Question 16 (the fission reactor question)
There seems to be bit of confusion on this forum about the speed of fission neutrons. In a typical atomic fission, the velocity of the neutrons is around 1 MeV (or about 10^7 metres per second). In order to interact effectively with the nucleus, their velocity (and hence their de Broglie matter wavelength) needs to be slowed to about 0.02 MeV. At these speeds, they almost in thermal equilibrium with their surroundings, and hence, they are referred to as "thermal neutrons". That is what the moderator does, it absorbs the momentum of the 1 MeV neutrons through multiple elastic collisions, until they are in thermal equilibrium with their surroundings. Anyway, the correct answer is (A) withdraw the control rods.

 

[fysiqs]

A 91-92 raw could still align to like a 96 cause it was so hard. That’s what I’m aiming for

You honestly have no idea about marks. A raw mark, as in a truly raw mark without school moderation, of 70% will be alligned to very high 80's. A raw mark of 91 would put you in the top 20 inthe state and would be given as 98 -99. The average RAWMARK in a physics exam is approx 55 in a good year. Just an fyi.

 

[Speed’o’sound Sonic]

You honestly have no idea about marks. A raw mark, as in a truly raw mark without school moderation, of 70% will be alligned to very high 80's. A raw mark of 91 would put you in the top 20 inthe state and would be given as 98 -99. The average RAWMARK in a physics exam is approx 55 in a good year. Just an fyi.

Guess we’ll find out Props to you though mate

 

[fysiqs]

View attachment 29434

If you guys still care about that exam, MC answers from High School Physics Explained are uploaded

I think this guy might be in trouble with NESA. As one of the senior markers in physics, there is the hilarious situation that he actually got some of these wrong. More worryingly, as a senior marker, he should not have discussed these answers with he general public, its actually against the rules of being a marker to discuss HSC marking and to do this before the marking begins is a big no-no.so I'm told.......... Especially with poor kids doing the chem exam today, they would be be annoyed at listening to his answers. Seems like he has caught the youtube bug of trying to be first with his "review". Hopefully Kerry Sheehan of NESA never finds out

 

[Speed’o’sound Sonic]

I think this guy might be in trouble with NESA. As one of the senior markers in physics, there is the hilarious situation that he actually got some of these wrong. More worryingly, as a senior marker, he should not have discussed these answers with he general public, its actually against the rules of being a marker to discuss HSC marking and to do this before the marking begins is a big no-no.so I'm told.......... Especially with poor kids doing the chem exam today, they would be be annoyed at listening to his answers. Seems like he has caught the youtube bug of trying to be first with his "review". Hopefully Kerry Sheehan of NESA never finds out

Chill

 

[Esdog07]

For question 20, there has been disputes over where it is A) or D). But I think I have a definitive case for why it is, in fact, A. When the ball undergoes a projectile-ish motion with the semi-circular ramp, it has both horizontal and vertical velocity components, right?

However! the centripetal force has a velocity component that is PERPENDICULAR to it. Considering the centripetal force is the Normal, this means the horizontal velocity component of the "projectile path" must be the velocity in the centripetal force, hence the centripetal force must be constant.

Also, remember, the centripetal force cannot have a velocity that is not constant--I don't think that makes sense.

So I'm a bit confused as to why MATRIX has set Q20 as D).

Ye that was my reasoning as well

 

[Speed’o’sound Sonic]

Guys Physics was 4 days ago now surely some official answers are out

 

[wizzkids]

How is 19 (A)? EMF is induced at the ends of the points perpendicular to the axis of the rod and hence no emf between p and q.

My bad ... there is a tiny emf induced in the through-thickness direction, but nothing end to end ... so the answer is (C) no e.m.f.

 

[fysiqs]

Guys Physics was 4 days ago now surely some official answers are out

Chill. I know, 4 whole days.

 

[wizzkids]

Matrix Education released their 2020 HSC Physics answers up if anyone is interested

In my humble opinion, I disagree with Matrix explanation for MCQ 20 being (D). The essence of the problem is that horizontal and vertical components of motion can be independently analysed. The vertical component of motion is subjected to only the constant gravitational force; on this point everyone seems to agree. The horizontal motion takes place in the horizontal plane, and it is uniform circular motion, around a path of constant radius. The centripetal acceleration and the centripetal force are towards the centre of curvature, and are constant. It is a logical error to say that a reduction in the vertical velocity will lower the centripetal acceleration - they are orthogonal. The final step, vector addition of the two force vectors, which are orthogonal. The magnitude of the resultant force is constant (but it's direction is constantly changing). (A) is correct

 

[black.mamba]

I think this guy might be in trouble with NESA. As one of the senior markers in physics, there is the hilarious situation that he actually got some of these wrong. More worryingly, as a senior marker, he should not have discussed these answers with he general public, its actually against the rules of being a marker to discuss HSC marking and to do this before the marking begins is a big no-no.so I'm told.......... Especially with poor kids doing the chem exam today, they would be be annoyed at listening to his answers. Seems like he has caught the youtube bug of trying to be first with his "review". Hopefully Kerry Sheehan of NESA never finds out

Wait damn what happened?? I couldn't find his vid yesterday, thought sth was up. Kinda feel bad for him bc i used his vids a lot throughout the past year.

Also which questions did he get wrong?

 

[JeydinNewWon]

Wait damn what happened?? I couldn't find his vid yesterday, thought sth was up. Kinda feel bad for him bc i used his vids a lot throughout the past year.

Also which questions did he get wrong?

That's strange. He must've deleted it or it had to be taken down. Still, his logic was correct in the multiple choice, especially with Question 20.

 

[Speed’o’sound Sonic]

That's strange. He must've deleted it or it had to be taken down. Still, his logic was correct in the multiple choice, especially with Question 20.

Might just be the multiple answers in q2 lol. Maybe NESA didn’t want answers out that early

 

[JeydinNewWon]

Might just be the multiple answers in q2 lol. Maybe NESA didn’t want answers out that early

Isn't NESA ironically validating his own answers at that point? Makes sense, this year's exams have been...weird to say the least.

 

[Speed’o’sound Sonic]

Isn't NESA ironically validating his own answers at that point? Makes sense, this year's exams have been...weird to say the least.

Oath. NESA has been super weird this year, and along with all the outages in ScienceExt they’ll have a very tough time marking this year. Hopefully it all works out fine though.

 

[JeydinNewWon]

Oath. NESA has been super weird this year, and along with all the outages in ScienceExt they’ll have a very tough time marking this year. Hopefully it all works out fine though.

I managed to find an unlisted link to the video. Turns out he took it down due him being a senior marker of Physics. This means his answers are qualified. He may not be an exam writer but his answers are definitely have the logic and he has qualified many years of Physics teaching experience.

 

[Speed’o’sound Sonic]

I managed to find an unlisted link to the video. Turns out he took it down due him being a senior marker of Physics. This means his answers are qualified. He may not be an exam writer but his answers are definitely have the logic and he has qualified many years of Physics teaching experience.

That’s interesting to hear. I wonder why they took the video down seems super odd... who knows?

 

[Fabrizio]

In my humble opinion, I disagree with Matrix explanation for MCQ 20 being (D). The essence of the problem is that horizontal and vertical components of motion can be independently analysed. The vertical component of motion is subjected to only the constant gravitational force; on this point everyone seems to agree. The horizontal motion takes place in the horizontal plane, and it is uniform circular motion, around a path of constant radius. The centripetal acceleration and the centripetal force are towards the centre of curvature, and are constant. It is a logical error to say that a reduction in the vertical velocity will lower the centripetal acceleration - they are orthogonal. The final step, vector addition of the two force vectors, which are orthogonal. The magnitude of the resultant force is constant (but it's direction is constantly changing). (A) is correct

You guys need to relax with this. Doesnt matter how many times you explain it, its not going to change NESA's answer when it comes out