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# AQA Physics PHYA4 - Thursday 11th June 2015 [Exam Discussion Thread] watch

1. (Original post by a.a.k)
What r u guys doing for optional unit.
I do 5D turning points

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Me too!! How you finding it? All the papers where standard questions from the old slyabus until last year so now I'm kinda worried :///

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2. (Original post by gcsestuff)
Attachment 420019

Hi can someone tell me if these graphs and the statements I've made at the right hand side are correct. Also do I need to know anymore graphs?

So;

For the velocity graph, the gradient is negative from a maximum when the displacement is to the right of the equilibrium as its trying to accelerate backwards towards the normal.

The gradients are different as velocity always opposes displacement?

And for acceleration its opposite as acceleration is always toward the equilibrium position so as its displaces +ve to the right its acceleration is towards the left -ve.

Sorry this is a bit muddled, but if someone could tell me if I'm correct or just make it a little easier that would be great thanks )))

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Attached Images

3. (Original post by gcsestuff)
Me too!! How you finding it? All the papers where standard questions from the old slyabus until last year so now I'm kinda worried :///

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I finf 5D easiest of them all

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4. For SHM if you have been given displacement: x(t)=Acos(omega.t) for eg. You can easily derive the trig waveforms for velocity and acceleration just by taking the time derivative.
dx/dt=v(t)=-AomegaSin(omega.t)
d^2x/dt^2 = a(t)=-A(omega)^2Cos(omega.t).
I find this easier when asked to draw curves for velocity/displacement/acceleration. You can go backwards through the anti-derivative.

Also this works for emf:
Nphi(t)=BANSin(omega.t) then
E=-dNphi(t)/dt which is just -BAN(omega)Cos(omega.t)

I find it easier to think of it mathematically, however, if you don't take maths then this will be useless
5. (Original post by Protoxylic)
For SHM if you have been given displacement: x(t)=Acos(omega.t) for eg. You can easily derive the trig waveforms for velocity and acceleration just by taking the time derivative.
dx/dt=v(t)=-AomegaSin(omega.t)
d^2x/dt^2 = a(t)=-A(omega)^2Cos(omega.t).
I find this easier when asked to draw curves for velocity/displacement/acceleration. You can go backwards through the anti-derivative.

Also this works for emf:
Nphi(t)=BANSin(omega.t) then
E=-dNphi(t)/dt which is just -BAN(omega)Cos(omega.t)

I find it easier to think of it mathematically, however, if you don't take maths then this will be useless
Hi yeah I do understand this I just struggle applying it this way, just the way I am

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6. (Original post by gcsestuff)
Hi yeah I do understand this I just struggle applying it this way, just the way I am

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Yeah, a lot of people don't find this way easy. But all I have to do is remember how to differentiate trig functions and apply chain rule and all of that I do in maths, so it's one less thing to remember.
7. As requested earlier, photos of the multiple choice sheet:
Attachment 420073420077Attachment 420073420077420100
(hopefully these have actually all uploaded successfully, the internet is not being cooperative)
So the real thing will obviously not be a bad photocopy, and the name section was added by our teacher, but this is how you fill in your answers for the multiple choice. A lot of people don't seem to have been made aware that this exists so make sure you leave enough time to fill it in in the exam!

There isn't a section for us to write details in, but the top right ("For office use only") appears to have our centre number and some random persons candidate number printed on it so I'm not sure if this is filled in by the college or something like that beforehand, or if the papers are just attached to the rest.
Attached Images

8. Any ideas for the 6 marker? I'm thinking maybe a question on an experiment, resonance, an explanation of 'potential' for both electric and gravitational fields or maybe induction and motors?
9. "Newton's third law states that when an object exerts a force on another object, there is an equal but opposite force exerted on the first object by the second".
If there are equal but opposite forces exerted on the bodies during interactions then the forces would cancel each other out and nothing would ever change their momentum! How true is that?
This question is from OCR but i cannot seem to find it now as my teacher gave it to us last year after finishing the course.

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10. (Original post by Mehrdad jafari)
"Newton's third law states that when an object exerts a force on another object, there is an equal but opposite force exerted on the first object by the second".
If there are equal but opposite forces exerted on the bodies during interactions then the forces would cancel each other out and nothing would ever change their momentum! How true is that?
This question is from OCR but i cannot seem to find it now as my teacher gave it to us last year after finishing the course.

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This is a very common mistake - the forces are acting on different bodies - force one acts on body two, force two acts on body one. If the forces are equal and opposite on the same body, then yes, they do cancel out, but otherwise they cause changes
11. (Original post by Mehrdad jafari)
"Newton's third law states that when an object exerts a force on another object, there is an equal but opposite force exerted on the first object by the second".
If there are equal but opposite forces exerted on the bodies during interactions then the forces would cancel each other out and nothing would ever change their momentum! How true is that?
This question is from OCR but i cannot seem to find it now as my teacher gave it to us last year after finishing the course.

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Object would come to rest if they were completely inelastic
In really life all objects are elestic.

Think rebounds

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12. (Original post by a.a.k)
Object would come to rest if they were completely inelastic
In really life all objects are elestic.

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13. (Original post by Disney0702)
Ah thanks a lot ☺ it'd be great if you could upload a picture, should you find it, because I don't think my teacher showed us.
Just posted it then thought I should probably have quoted you in! It's on the page before this post

14. Can someone read this and make sure it makes sense and add to it if possible thanks )

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15. (Original post by Lau14)
Just posted it then thought I should probably have quoted you in! It's on the page before this post
What year ud this for

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16. (Original post by Lau14)
Just posted it then thought I should probably have quoted you in! It's on the page before this post
Thank you so much Lauren!

I've definitely never seen this before! Had you never uploaded this I would've probably freaked out in the exam hall.

And the attachment you released is in good condition.
17. (Original post by Lau14)
This is a very common mistake - the forces are acting on different bodies - force one acts on body two, force two acts on body one. If the forces are equal and opposite on the same body, then yes, they do cancel out, but otherwise they cause changes
Thanks, but how can the forces exerted on different bodies, as if you push a car for example, not cancel each other when the force and the reaction are equal? Also can you give an example where the forces would cancel each other out? Thank you

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18. Hello everyone!

I was wondering if anyone could help me with Q8 Jun '06 in the following link.

My answer was D but the correct answer is C and I cannot see how.

19. (Original post by Lau14)
As requested earlier, photos of the multiple choice sheet:
Attachment 420073420077Attachment 420073420077420100
(hopefully these have actually all uploaded successfully, the internet is not being cooperative)
So the real thing will obviously not be a bad photocopy, and the name section was added by our teacher, but this is how you fill in your answers for the multiple choice. A lot of people don't seem to have been made aware that this exists so make sure you leave enough time to fill it in in the exam!

There isn't a section for us to write details in, but the top right ("For office use only") appears to have our centre number and some random persons candidate number printed on it so I'm not sure if this is filled in by the college or something like that beforehand, or if the papers are just attached to the rest.
I have never seen this before. Are we supposed to tick the answers on this sheet?

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20. mom before = 8000x2.5=20,000kgms

mom after = (8000+12000)x2.5=50,000kgms

50k-20k=30k but thats not on the answer what am i doing wrong😢

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