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

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.

Reply 382

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. :biggrin:

(edited 8 years ago)

Reply 383

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. :biggrin:

But we are told that the brakes are applied.

Reply 384

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.

:biggrin:

Reply 385

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.

:biggrin:

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 :smile:

.
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.

Reply 386

a123a

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 :smile:

.
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?

Reply 387

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 :smile:

.
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.

Reply 388

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.

Reply 389

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. :/

Reply 390

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.

Reply 391

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

Reply 392

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

Reply 393

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.

Reply 394

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.

(edited 8 years ago)

Reply 395

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?
:biggrin:

Reply 396

Hilton184

9

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?
:biggrin:

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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Reply 397

Elcor