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# OCR A Physics G481 Jan 12th 2012 Tweet

Physics exam discussion - share revision tips in preparation for GCSE, A Level and other physics exams and discuss how they went afterwards.

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1. Re: OCR A Physics G481 Jan 12th 2012
(Original post by Maxie)
Cant remember... but I made work done equal to Loss in Ke then just found the value for initial Ke and Divided it By the 200m; which was the depth of the crater.
thing is i did the same and thought it was too simple for 3 marks.. so i found deceleration of the asteroid using a=(v^2-u^2)/2s and then times that by the mass of the asteroid(f=ma) :/ I dunno if that is right at all
2. Re: OCR A Physics G481 Jan 12th 2012
(Original post by Maxie)
I meant that Regardless of the mass the acceleration is always the same.. which Galileo proved. Because as Mass increases so does the force acting on it i.e. its weight.
Allthough Galileo proved this as free fall a fixed acceleration so the mass has no effect because A is the same. but in the paper its a trolley on ground level so as mass increases the weight acting down is increases thus accelerating the trolley more. because on ground level am object can keep accelerating until the speed of light but then the mass is infinite.
Last edited by james.odedra; 12-01-2012 at 18:42. Reason: missed something out
3. Re: OCR A Physics G481 Jan 12th 2012
(Original post by shorty.loves.angels)
Blanked on this one... totally didn't put heat energy
You may get a mark, there will almost certainly be some heat! Imagine the friction of a meteor hitting earth
4. Re: OCR A Physics G481 Jan 12th 2012
(Original post by shorty.loves.angels)
I definitely made some careless errors, didn't have enough time to check through though.
This. I literally just finished, started flicking through to make sure I had done all the questions and "pens down"
5. Re: OCR A Physics G481 Jan 12th 2012
(Original post by james.odedra)
Allthough Galileo proved this as free fall a fixed acceleration so the mass has no effect because A is the same. but in the paper its a trolley on ground level so as mass increases the weight acting down is increases thus accelerating the trolley more.
falileo proved that all objext accelerate toward the ground at the same rate,
6. Re: OCR A Physics G481 Jan 12th 2012
Allthough Galileo proved this as free fall a fixed acceleration so the mass has no effect because A is the same. but in the paper its a trolley on ground level so as mass increases the weight acting down is increases thus accelerating the trolley more.
Even though there is a slope involed, the Force is the weight of the trolley. Therefore that cancels with the mass to give the same acceleration no matter what the weight was
7. Re: OCR A Physics G481 Jan 12th 2012
(Original post by james.odedra)
Allthough Galileo proved this as free fall a fixed acceleration so the mass has no effect because A is the same. but in the paper its a trolley on ground level so as mass increases the weight acting down is increases thus accelerating the trolley more.

The trolley does not accelerate more. The intervals would be exactly the same. The component down the slope is mgsinx, where x is the angle between the slope and level ground. Using F=ma, we get mgsinx=ma. The m's cancel therefore the acceleration is unaffected by the mass of the trolley.
8. Re: OCR A Physics G481 Jan 12th 2012
so it was two marks right?
I got:
- Same acceleration
- Because all object accelerate toward the ground at the same rate.

How many marks I get?
9. Re: OCR A Physics G481 Jan 12th 2012
On the seatbelt question, I put that it also means the driver hits the airbag at the correct time, as I read this in my textbook, do you think I will get a mark for this? :s

(I put about braking force and stuff too )
10. Re: OCR A Physics G481 Jan 12th 2012
(Original post by alizasauras)
On the seatbelt question, I put that it also means the driver hits the airbag at the correct time, as I read this in my textbook, do you think I will get a mark for this? :s

(I put about braking force and stuff too )
no lol
I saw it too in the textbookk, but the textbook is not good
11. Re: OCR A Physics G481 Jan 12th 2012
(Original post by Namod)
so it was two marks right?
I got:
- Same acceleration
- Because all object accelerate toward the ground at the same rate.

How many marks I get?

Not sure... The same acceleration bit is right, but not all objects accelerate towards the ground at the same rate - in this question the trolleys were going down a slope - they would not be accelerating towards the ground as fast as an object in free fall. It will depend on how you worded it and what the mark scheme is looking for. As I don't have the mark scheme, I can't really give you a useful answer.
12. Re: OCR A Physics G481 Jan 12th 2012
On the crater one, where it said it has created a 200m deep crater, all I did was:

Work Done to stop the meteor = kinetic energy
so
200m X F = 8x10^16 or whatever it was..

Is this right? it seemed to little for 3 marks and i've realized you might have had to consider the 200m lost in Gravitational potential energy.
13. Re: OCR A Physics G481 Jan 12th 2012
(Original post by 4ever_drifting)
Not sure... The same acceleration bit is right, but not all objects accelerate towards the ground at the same rate - in this question the trolleys were going down a slope - they would not be accelerating towards the ground as fast as an object in free fall. It will depend on how you worded it and what the mark scheme is looking for. As I don't have the mark scheme, I can't really give you a useful answer.
In one of the mark schemes of galileo's experiment question had:
"all objects accelerate towards the ground at the same rate" for a mark
so I will just get one mark?
14. Re: OCR A Physics G481 Jan 12th 2012
(Original post by Miryo)
On the crater one, where it said it has created a 200m deep crater, all I did was:

Work Done to stop the meteor = kinetic energy
so
200m X F = 8x10^16 or whatever it was..

Is this right? it seemed to little for 3 marks and i've realized you might have had to consider the 200m lost in Gravitational potential energy.
me too but now i know its wrong
15. Re: OCR A Physics G481 Jan 12th 2012
(Original post by Namod)
In one of the mark schemes of galileo's experiment question had:
&quot;all objects accelerate towards the ground at the same rate&quot; for a mark
so I will just get one mark?
All objects in free fall, ignoring air resistance, accelerate towards the ground at the same rate. Consider a steep slope and a shallow slope though - would you expect objects to fall down them at the same rate?

As I say though I don't have a markscheme, and you may well get two marks, or you might not, I can't give a definitive answer either way.
16. Re: OCR A Physics G481 Jan 12th 2012
(Original post by Namod)
me too but now i know its wrong
it gives the same answer if you used suvat so I think it might be right actually...just checked it now,
17. Re: OCR A Physics G481 Jan 12th 2012
On the crater one, where it said it has created a 200m deep crater, all I did was:

Work Done to stop the meteor = kinetic energy
so
200m X F = 8x10^16 or whatever it was..

Is this right? it seemed to little for 3 marks and i've realized you might have had to consider the 200m lost in Gravitational potential energy.
Did you get 3*10^14?

i found out a to put into F=ma
18. Re: OCR A Physics G481 Jan 12th 2012
(Original post by Miryo)
On the crater one, where it said it has created a 200m deep crater, all I did was:

Work Done to stop the meteor = kinetic energy
so
200m X F = 8x10^16 or whatever it was..

Is this right? it seemed to little for 3 marks and i've realized you might have had to consider the 200m lost in Gravitational potential energy.
i used SUVAT too find the deceleration of the meteor, and then timesd that by mass (F=ma) to find force. spoken too some peeps doing a2 who did the exam and thats what they did. i originaly did what you did but like you thought it was too little and did it that way. plus they gave you initial speed so i think that was a prompt to use suvat.. still a tad unsure though you may well be right.

19. Re: OCR A Physics G481 Jan 12th 2012
(Original post by Maxie)
I definitely got 10^9 too
(Original post by drewb)
I'm sure I got the young's modulus as some gigantic number, possibly 7x10^9?
Yeah me too, but I don't think it's right. Earlier discussion showed that we divided area by 1000 and not (1000 x 1000) as it was mm^2 to m^2
20. Re: OCR A Physics G481 Jan 12th 2012
how to work out the speed one?
I did 0.5 x m x v^2 = kinetic energy
and find v with it but got 2.3 x 10^4
and answer was 2.0 x 10^4
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