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OCR Physics A G484 - The Newtonian World - 11th June 2015

i only knew it was resonance because of the pencil mark lol
you had to draw a peak and label it natural frequency

then just explain resonance and say amplitude is maximum

Bollox
I did a acc-f graph
Goodbye 3 marks
Goodbye A
Goodbye uni

Reply 1561

randlemcmurphy

11

Original post by MMB07

Question 2: State in words the law used to determine your answer to i)

Mark scheme from OCR: DO NOT ALLOW NEWTON'S 2nd LAW, as in question 1 we claimed that newton was wrong

Newton wasn't wrong, the persons statement was incorrect.

Reply 1562

ETRC

17

Original post by leroythelost

What grade do you need in physics overall? I need an A and I got 34/40 for practical skills

i need an A too.

i got like 252/300 last year
if i scrape an A on this that's 72ums and i think my practical will be a C which is 40. So i'll need a very high B in g485.

If G485 is normal like other years then I can get an A comfortably but I don't think it will be normal so i am scared.

Reply 1563

L'Evil Fish

OP

18

Original post by Jackasnacks

Bollox
I did a acc-f graph
Goodbye 3 marks
Goodbye A
Goodbye uni

Lol I did a frequency against V max graph

Reply 1564

ETRC

17

Original post by randlemcmurphy

Newton wasn't wrong, the persons statement was incorrect.

who said Newton was wrong lmao
and they claim to know the mark scheme

Reply 1565

ibanezmatt13

2

So was it Newton's second law that we needed to state that we used in i) ?

Reply 1566

rosstoal

1

Original post by sagar448

Was it conservation of momentum when we were working out the acceleration of the spacecraft? PLEASE TELL ME IT WAS

I put it was newtons 3rd (equal and opposite forces).
Because I found the initial acceleration of the xenon ions, the multiplied by their mass to get the force the exert in their direction.
Then due to Newtons 3rd, the spaceship experiences the same force. Then divide that same force by the mass of the spaceship to get its Acceleration

Anyone do the same?

Reply 1567

FummyJr

1

Original post by MMB07

Question 2: State in words the law used to determine your answer to i)

Mark scheme from OCR: DO NOT ALLOW NEWTON'S 2nd LAW, as in question 1 we claimed that newton was wrong

They want you to describe newtons 2nd law, they are just saying you wont get the marks for just writing the name of the law.

Reply 1568

sagar448

4

Original post by L'Evil Fish

Lol I did a frequency against V max graph

Dude what did you say for you know when the question asked why the temperature will take longer to rise in real?

I said the heat is lost to the surrounding since it isn't insulated or whatever didn't know second reason?

Reply 1569

Elcor

14

Original post by FummyJr

They want you to describe newtons 2nd law, they are just saying you wont get the marks for just writing the name of the law.

Original post by ibanezmatt13

So was it Newton's second law that we needed to state that we used in i) ?

Original post by rosstoal

I put it was newtons 3rd (equal and opposite forces).
Because I found the initial acceleration of the xenon ions, the multiplied by their mass to get the force the exert in their direction.
Then due to Newtons 3rd, the spaceship experiences the same force. Then divide that same force by the mass of the spaceship to get its Acceleration

Anyone do the same?

I said conservation of linear momentum.

Reply 1570

ETRC

17

Original post by Jackasnacks

Bollox
I did a acc-f graph
Goodbye 3 marks
Goodbye A
Goodbye uni

that's not as bad as what i did

i messed up 6 easy marks on shm questions- my brain just decided to quit
and i completely forgot about direction in momentum

i don't even know why the questions were worded so crap

Reply 1571

trooken

2

Original post by rosstoal

I put it was newtons 3rd (equal and opposite forces).
Because I found the initial acceleration of the xenon ions, the multiplied by their mass to get the force the exert in their direction.
Then due to Newtons 3rd, the spaceship experiences the same force. Then divide that same force by the mass of the spaceship to get its Acceleration

Anyone do the same?

Such a confusing question. Depending on how you look at it, it could be conservation of momentum, Newton's 2nd or 3rd law

Reply 1572

Elcor

14

Original post by sagar448

Dude what did you say for you know when the question asked why the temperature will take longer to rise in real?

I said the heat is lost to the surrounding since it isn't insulated or whatever didn't know second reason?

Not all the photons would be adsorbed by the titanium, some would be reflected.

Reply 1573

ibanezmatt13

2

Original post by rosstoal

I put it was newtons 3rd (equal and opposite forces).
Because I found the initial acceleration of the xenon ions, the multiplied by their mass to get the force the exert in their direction.
Then due to Newtons 3rd, the spaceship experiences the same force. Then divide that same force by the mass of the spaceship to get its Acceleration

Anyone do the same?

I said that rate of change of momentum of ions remained constant, as constant exhaust velocity. And since force is rate of change of momentum, and system is closed, net force on rocket is constant.

Acceleration inversely proportional to mass. Mass decreases as ions emitted, so acceleration increases.

However didn't mention the point "total momentum is conserved" so probs lost a mark :/

Reply 1574

BrokenS0ulz

3

you know when we had to derive keplers third law, was that basically v=2pir/T, F=mv^2/r stuff, equating them and then subbing into F =GMm/r^2?

Reply 1575

L'Evil Fish

OP

18

Original post by sagar448

Dude what did you say for you know when the question asked why the temperature will take longer to rise in real?

I said the heat is lost to the surrounding since it isn't insulated or whatever didn't know second reason?

Lol I said photo electric effect causing emission of electrons

Didn't say about work function though, so they might assume some KE which would heat it up

But it's probably some photons reflected or something for second