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

Alex621
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#381
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(Original post by randlemcmurphy)
We are told the aircraft is not moving, so it has to have a component to balance the weight and the force produced by the engine, hence it is at an angle.
I got confused about this as well as I thought the force to prevent it moving forwards would be provided by the brakes?
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randlemcmurphy
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(Original post by AlexParmenter)
I got confused about this as well as I thought the force to prevent it moving forwards would be provided by the brakes?
That is a very good point. That does confuse things rather.
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sagar448
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(Original post by AlexParmenter)
I got confused about this as well as I thought the force to prevent it moving forwards would be provided by the brakes?
Well let's assume that the brakes aren't pressed. So the rockets provide a forward force and the weight is downwards. So why is the resultant at an angle and why isn't the aircraft moving?

Consider the forces. The weight pushes on the ground while the ground pushes back up.
There is a forward force on the ground provided by the wheels of the aircraft which comes from the rockets but the ground pushes back with the same equal force. So the resultant force provided by the aircraft is still and at an angle.
Fnet = 0 for the whole SYSTEM.
So newtons third law.
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randlemcmurphy
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(Original post by sagar448)
Well let's assume that the brakes aren't pressed. So the rockets provide a forward force and the weight is downwards. So why is the resultant at an angle and why isn't the aircraft moving?

Consider the forces. The weight pushes on the ground while the ground pushes back up.
There is a forward force on the ground provided by the wheels of the aircraft which comes from the rockets but the ground pushes back with the same equal force. So the resultant force provided by the aircraft is still and at an angle.
Fnet = 0 for the whole SYSTEM.
So newtons third law.
But we are told that the brakes are applied.
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sagar448
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(Original post by randlemcmurphy)
But we are told that the brakes are applied.
Oh I see did not realise brakes were applied sorry about that. I looked at the question again and I suppose since they made us label only two force, weight and the force from the engine, I guess we ignore the braking force (which if it was taken into account would be equal and opposite to the force from the engine). So looking at the engine force and the weight force the resultant would be at an angle.

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randlemcmurphy
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(Original post by sagar448)
Oh I see did not realise brakes were applied sorry about that. I looked at the question again and I suppose since they made us label only two force, weight and the force from the engine, I guess we ignore the braking force (which if it was taken into account would be equal and opposite to the force from the engine). So looking at the engine force and the weight force the resultant would be at an angle.

To be honest I would have drawn the force at the angle, the only reason why because I wouldn't have even read the "brakes are applied" part so I wouldn't question it .
On another note, hopefully because last year they tested the specific heat capacity experiment, they don't test it again this year, as that is my worst practical to write about.
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a123a
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(Original post by randlemcmurphy)
To be honest I would have drawn the force at the angle, the only reason why because I wouldn't have even read the "brakes are applied" part so I wouldn't question it .
On another note, hopefully because last year they tested the specific heat capacity experiment, they don't test it again this year, as that is my worst practical to write about.
What other practicals are there?
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sagar448
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(Original post by randlemcmurphy)
To be honest I would have drawn the force at the angle, the only reason why because I wouldn't have even read the "brakes are applied" part so I wouldn't question it .
On another note, hopefully because last year they tested the specific heat capacity experiment, they don't test it again this year, as that is my worst practical to write about.
Yeah during the mock I didn't even realise it said the brakes are applied but I still knew that the aircraft wasn't moving. Yeah same, it's one of the most annoying things about G484. I doubt it will be on the exam this year but I think the exams are going to be SUPER hard since the G481 people said was tough and the C2.
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randlemcmurphy
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(Original post by sagar448)
Yeah during the mock I didn't even realise it said the brakes are applied but I still knew that the aircraft wasn't moving. Yeah same, it's one of the most annoying things about G484. I doubt it will be on the exam this year but I think the exams are going to be SUPER hard since the G481 people said was tough and the C2.
I resat G481, to be honest it wasn't that bad, as long as you had a grasp on the main concepts you were fine, quite a fair bit of calculations, not too many written answers, the main one being 4 marks on an experiment. Actually one of the questions was similar to one asked in the old spec, so maybe look over some old spec questions for G484. The only odd thing about G481 was that there were no easy definition questions (the first question was easy though, just labeling axis), the only definition question you were not allowed to explain it via the formula. So I would recommend making sure you know most definitions just in case.
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sagar448
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(Original post by randlemcmurphy)
I resat G481, to be honest it wasn't that bad, as long as you had a grasp on the main concepts you were fine, quite a fair bit of calculations, not too many written answers, the main one being 4 marks on an experiment. Actually one of the questions was similar to one asked in the old spec, so maybe look over some old spec questions for G484. The only odd thing about G481 was that there were no easy definition questions (the first question was easy though, just labeling axis), the only definition question you were not allowed to explain it via the formula. So I would recommend making sure you know most definitions just in case.
Oh that sounds a bit more relieving. So I mean what do you think? Will it be hard? Looking at the previous years it is getting harder each year but the January 2013 was harder than the June 2014 so I can't really tell. :/
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randlemcmurphy
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(Original post by sagar448)
Oh that sounds a bit more relieving. So I mean what do you think? Will it be hard? Looking at the previous years it is getting harder each year but the January 2013 was harder than the June 2014 so I can't really tell. :/
I agree they do seem to be getting harder. Question 4a from June 2014 stumped me, got 1/2 marks, one of the points is so obvious but I would never have thought to have written it (orbiting in same direction of planet rotates). To be honest I find G484 and G485 easier than G481 and definitely G482. The papers seem slightly more "predictable", I just hope we don't have a hard calculation question like that photographing of Earth's surface one you got a bit stumped on.
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sagar448
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(Original post by randlemcmurphy)
I agree they do seem to be getting harder. Question 4a from June 2014 stumped me, got 1/2 marks, one of the points is so obvious but I would never have thought to have written it (orbiting in same direction of planet rotates). To be honest I find G484 and G485 easier than G481 and definitely G482. The papers seem slightly more "predictable", I just hope we don't have a hard calculation question like that photographing of Earth's surface one you got a bit stumped on.
Oh yes I remember question 4a I got half the marks too didn't know about the orbiting in same direction of planet rotation either. That one was quite annoying. You are spot on about G484 and G485 being easier than last year because I feel the same way. I am retaking G482 and while going through the PP I got stuck so many times but in G485 i'm usually racing through the questions. To be honest I'm a lot more scared about G484 than G485 or G482 because I'm always scraping my grade and it's a small unit so there are like a billion possibilities of questions. In the G484 mock (June 2014) I got an A, very close to an A*. I went home looked at the paper again and I could have definitely done better and probably gotten an A*. So I'm hoping this situation doesn't happen for the real exam :C
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verello12
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Do we have to know suvat equations for this exam cause I didn't see it in the spcification but in the 2014 paper there is a question where we got to use suvat
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randlemcmurphy
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(Original post by verello12)
Do we have to know suvat equations for this exam cause I didn't see it in the spcification but in the 2014 paper there is a question where we got to use suvat
Well we could have synoptic questions, however the suvat equations are in the formula booklet.
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verello12
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Quick question guys, when calculating numerical answers how much do we round off the numbers? Is 3SF the standard?

Also when doing a second part of a question where we have to use the answer from the previous question, do we use the rounded up answer or the full number?

Would we get marks taken off if we don't round up and just write down the full answer.
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sagar448
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(Original post by verello12)
Quick question guys, when calculating numerical answers how much do we round off the numbers? Is 3SF the standard?

Also when doing a second part of a question where we have to use the answer from the previous question, do we use the rounded up answer or the full number?

Would we get marks taken off if we don't round up and just write down the full answer.
Usually the decimal place or the significant figure could be used from the numericals in the question itself.

Second part of the question, always use the full number and then use the sigfig from the question or the sigfig from the answer above.

Marks are taken off if too many decimal places used or significant figures used.

This is my opinion anyways, what do other people think?
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Hilton184
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(Original post by sagar448)
Usually the decimal place or the significant figure could be used from the numericals in the question itself.

Second part of the question, always use the full number and then use the sigfig from the question or the sigfig from the answer above.

Marks are taken off if too many decimal places used or significant figures used.

This is my opinion anyways, what do other people think?
Marks are not taken off if too many significant figures are used. You could put to calculator value if you wanted to. It says at top of Mark schemes something like 'if data is given to 2sf, allow answers to 2 or more sf'.

I usually use full calculator values from previous answers in subsequent answers, and on answer lines write to 3sf. Last year I used to worry so much about this and always got worked up about it, but I've realised it really doesn't matter as long as you don't use 1 significant figure haha.


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Elcor
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(Original post by Hilton184)
Marks are not taken off if too many significant figures are used. You could put to calculator value if you wanted to. It says at top of Mark schemes something like 'if data is given to 2sf, allow answers to 2 or more sf'.

I usually use full calculator values from previous answers in subsequent answers, and on answer lines write to 3sf. Last year I used to worry so much about this and always got worked up about it, but I've realised it really doesn't matter as long as you don't use 1 significant figure haha.


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I think it's best to incorporate rounding errors, as sometimes your answer can disagree with the mark scheme by the 2nd s.f. if you use exact values through many parts. Also if in your working you put '3.4' but actually use '3.353568...' and end up with a different answer, the examiner might think you've made a calculator error.

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Hilton184
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(Original post by Elcor)
I think it's best to incorporate rounding errors, as sometimes your answer can disagree with the mark scheme by the 2nd s.f. if you use exact values through many parts. Also if in your working you put '3.4' but actually use '3.353568...' and end up with a different answer, the examiner might think you've made a calculator error.

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Yeah I always write my full numbers down that I sub in to make it clear.
I think the older Mark schemes, from 2011 for example, don't really make note to the examiners enough about what values should be accepted.
But using the full value is always going to be acceptable I would think.

But like I said at the top of Mark schemes it says answers should be accepted to 2sf or more, so from that examiners should understand that different significant figures used in answers will lead to different values slightly in subsequent answers. Maybe it comes under ecf even though no marks would be lost.

But it's such a minor issue really.


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Username13
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Can someone explain specific heat capacity please?
If there's a lower specific heat capacity, why does temperature of the object fall more quickly?
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