Physics marathon (hsc) (7 Viewers)

[deswa1]

I found these questions hard (effing motors and gens ). Can you guys explain how to work them out (it'll be good practice for the marathon too):

http://www4.boardofstudies.nsw.edu....wer=D&courseID=15330&testQuestionID=300371900

http://www4.boardofstudies.nsw.edu....wer=B&courseID=15330&testQuestionID=300371901

Thanks heaps

 

[nerdasdasd]

My schools paper must of have been easy .....too easy. (rank 500).

 

[someth1ng]

I found these questions hard (effing motors and gens ). Can you guys explain how to work them out (it'll be good practice for the marathon too):

http://www4.boardofstudies.nsw.edu....wer=D&courseID=15330&testQuestionID=300371900

http://www4.boardofstudies.nsw.edu....wer=B&courseID=15330&testQuestionID=300371901

Thanks heaps

The one with the answer is C is quite easy. You need to know that in a semiconductor, there are two forms of currents - hole current and electron current which move in opposite directions and have opposite charge. If you do the right-hand rule, as positive and negative move in opposite direction, they will cause a force in the same direction.

For the dynamo one, you need to know that the change of flux will induce an emf (and current) such that it opposes the motion of the disc. In the disc, it will be from the axle down to the Y brush. The direction of current is shown using the EXTERNAL CIRCUIT. Therefore, Y to X.

 

[deswa1]

The one with the answer is C is quite easy. You need to know that in a semiconductor, there are two forms of currents - hole current and electron current which move in opposite directions and have opposite charge. If you do the right-hand rule, as positive and negative move in opposite direction, they will cause a force in the same direction.

Ahh shit- thanks bro. Yeah I knew there were the two types of current but I forgot that they travelled in opposite directions

 

[GoldyOrNugget]

i found this f**ucked question :|
"Determine the best strategy for each player in the following two-player game. There
are three piles, each of which contains some number of coins. Players alternate turns,
each turn consisting of removing any (non-zero) number of coins from a single pile.
The goal is to be the person to remove the last coin(s)."

eeeeeeekkkkkkkk :/

oh well theres always next year: physics vs. <<- ME

This is a fundamental game theory problem called Nim. If it's your go, take the bitwise exclusive-or operation of the binary representations of the number of coins in each pile, and and the result will be (iirc) the number of coins you should subtract from a pile. Or something like that, I haven't touched game theory in a while. Dunno what this is doing on a physics thread.

Do informatics guys!

 

[Keelan134]

With that cannonball question isn't that just a Newton thought experiment to explain the concept of escape velocity? If the cannon is powerful enough to launch it to the poles then due to the curvature of the earth and the excessive speed of the cannonball, then it will never return to earth and remain in orbit around the earth?

Dont mind me I'm just an average Physics kids, Internal Mark of 72 %

 

[nerdasdasd]

With that cannonball question isn't that just a Newton thought experiment to explain the concept of escape velocity? If the cannon is powerful enough to launch it to the poles then due to the curvature of the earth and the excessive speed of the cannonball, then it will never return to earth and remain in orbit around the earth?

Dont mind me I'm just an average Physics kids, Internal Mark of 72 %

Wouldnt it fall back to earth due to orbital decay ? How is it gonna maintain the orbital velocity ?

 

[deswa1]

These questions piss me off: http://www4.boardofstudies.nsw.edu....wer=B&courseID=15330&testQuestionID=300377963

From the HSC's point of view- do slotted tubes have eddy currents or not? It seems inconsistent because here they are assuming that there are no eddy currents induced whilst in transformers, you laminate them in order to reduce eddy currents, no eliminate them, implying that they still exist just in a weakened form.

 

[nerdasdasd]

These questions piss me off: http://www4.boardofstudies.nsw.edu....wer=B&courseID=15330&testQuestionID=300377963

From the HSC's point of view- do slotted tubes have eddy currents or not? It seems inconsistent because here they are assuming that there are no eddy currents induced whilst in transformers, you laminate them in order to reduce eddy currents, no eliminate them, implying that they still exist just in a weakened form.

Wouldn't slotted tubes just prevent eddy currents building up ? So yes in much weaker forms.

 

[Keelan134]

Wouldnt it fall back to earth due to orbital decay ? How is it gonna maintain the orbital velocity ?

It probably will, that would be how you would conclude it. So add, however the body will encounter air resistance resulting in thermal energy decreasing its orbit and returning to Earth. But anyways, this was just a thought experiment of Newton, that if he launched his cannonball fast enough, combined with the curvature of the earth it would never return and orbit, or if it was fast enough, it would escape completely. http://img.bhs4.com/db/9/db981489fa57715519cd9f0c467ad54cb38b9cc3_large.jpg

 

[someth1ng]

These questions piss me off: http://www4.boardofstudies.nsw.edu....wer=B&courseID=15330&testQuestionID=300377963

From the HSC's point of view- do slotted tubes have eddy currents or not? It seems inconsistent because here they are assuming that there are no eddy currents induced whilst in transformers, you laminate them in order to reduce eddy currents, no eliminate them, implying that they still exist just in a weakened form.

In real life, B is the correct answer but in terms of slotted things for HSC, there are still induced eddy currents but are smaller and cause NO braking.

 

[someth1ng]

It probably will, that would be how you would conclude it. So add, however the body will encounter air resistance resulting in thermal energy decreasing its orbit and returning to Earth. But anyways, this was just a thought experiment of Newton, that if he launched his cannonball fast enough, combined with the curvature of the earth it would never return and orbit, or if it was fast enough, it would escape completely. http://img.bhs4.com/db/9/db981489fa57715519cd9f0c467ad54cb38b9cc3_large.jpg

That's not what the question was asking, it said that it could make it to the north pole but what would occur as the ball is flying there.

deswa1 was the on the right track the first time.

 

[kenkap]

you should focus on the option, because that makes up 60% of the paper this year (new format). anyway aslong as you study you will do i know it.

never knew this...

 

[enoilgam]

Guys, this is a marathon thread (i.e. ask a question, answer the question etc). Please refrain from posting irrelevant content.

 

[kenkap]

is it true that they are changing the format???

 

[deswa1]

is it true that they are changing the format???

No. The format will be the same- 20 MC, 55 short answer, 25 option

 

[Azure]

Guys, this is a marathon thread (i.e. ask a question, answer the question etc). Please refrain from posting irrelevant content.

Take heed of this please.

 

[lovely_girl_290]

A very powerful cannon is able to shoot a 1kg cannon ball from the equator all the way to either of the geographical poles. The cannon is pointed to the geographical north pole and is fired.

Describe what occurs and explain why the ball does or doesn't reach the geographical north pole.

I think It will not reached the north pole because the force of the earth's rotation cause the ball to be deflected to the right of the pole (Coriolis effect)

 

[miss giggles]

Sorry, just a question. Wouldn't a decrease in rotational velocity result in a lower radius and hence an increased value of g?

Yeah that's what I thought too

 

[grizzlybear]

find the co-efficient of friction if and object begins to slide on an incline at 36 degree.
Compare coefficient of static friction with coefficient of kinetic friction