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# AQA Physics PHYA4 - 20th June 2016 [Exam Discussion Thread] watch

1. (Original post by SirRaza97)
We talk about uniform magnetic fields in our spec so the flux density remains the same at different distances.

So the radius is proportional to the velocity. B remains the same at different radii
Yeah I though so, just wanted to check, this caught me out on the june 12 paper question about the LHC.

You have any idea about how gravitational potentials caused by a mass is affected by another mass being added to a system?

Do potentials add or subtract....Im sure Ive seen an MC question like this regarding electric potential
2. http://filestore.aqa.org.uk/subjects...2-QP-JUN12.PDF
http://filestore.aqa.org.uk/subjects...W-MS-JUN12.PDF

Question 1 b) (ii) and (iii)

surely the units here when multiplying kg/s and m/s they would just give you (N) rather than momentum per second (Ns) and they later do for part (iii) where you can see 1.68 is now in newtons?

something small but the units don't make sense to me, any help appreciated
3. (Original post by SirRaza97)
First think which one is more positve and which is more negative relative to each other. Then it's a basic + to - radial ellectric field.
The right one is more positve but idk how to sketch it?
4. Can someone give me the perfect AQA definition of Gravitaional potential energy please
5. No problem

(Original post by boyyo)

Where you said to think about gravitational potential, A says potential energy, so how did you know to use gravitational potential?
by gravitational potential, I mean gravitational potential energy. You are probably wondering why I didnt use Ep=GMm/r, I dont really like that equation. If you use Ep=mgh, when h is higher, Ep is higher. So as you get closer to earth, your Ep falls.

(Original post by boyyo)

Also even using gravitiational potential, isnt it still inversely proportional to r aswell?
I was on about g=GM/r^2, not g=-change in V/change in r (which is another equation I dont like haha).
6. (Original post by boyyo)
Can someone give me the perfect AQA definition of Gravitaional potential energy please
gravitation potential is the work done per unit mass to move a small test mass from infinity to that point in a gravitational field.
7. (Original post by philo-jitsu)
Yeah I though so, just wanted to check, this caught me out on the june 12 paper question about the LHC.

You have any idea about how gravitational potentials caused by a mass is affected by another mass being added to a system?

Do potentials add or subtract....Im sure Ive seen an MC question like this regarding electric potential
yh I remember seeing something like that too. I think they add, but the + and - cancel to make them subtract
8. (Original post by duncant)
gravitation potential is the work done per unit mass to move a small test mass from infinity to that point in a gravitational field.
Ah ok, what about Gravitational potential energy?
9. (Original post by duncant)
No problem

by gravitational potential, I mean gravitational potential energy. You are probably wondering why I didnt use Ep=GMm/r, I dont really like that equation. If you use Ep=mgh, when h is higher, Ep is higher. So as you get closer to earth, your Ep falls.

I was on about g=GM/r^2, not g=-change in V/change in r (which is another equation I dont like haha).
lol ok i get you now. Just another quick question, can you use Ep=mgh, when its over large distances?
10. does anyone have a list of units we have to know such as 'k' for spring constant or something like that?
11. (Original post by boyyo)
lol ok i get you now. Just another quick question, can you use Ep=mgh, when its over large distances?
nah since g will change over large distances. and sorry didnt read your question, gravitational potential energy is the energy an object possesses due to the fact it is in a gravitation field
12. (Original post by philo-jitsu)
I may be wrong here but isnt the forces on both vertical sides kind of directed inwards...?

would the coil even rotate if it wasnt already moving, what I mean is the forces direction is perpendicular to the horizontal so how would they even rotate?..

I may be over complicating it
Your first point is right. The forces are inwards and along the same line of action. Hence they cause no torque
13. (Original post by duncant)
nah since g will change over large distances. and sorry didnt read your question, gravitational potential energy is the energy an object possesses due to the fact it is in a gravitation field
ahh cool, thanks man
14. Is anyone having trouble doing past papers in time cause I am. What can I do to improve I know day before the exam. 😅🔫
15. Hey Guys

Any tips on how to manage time in the exam? I.e answer the paper first and get to the multi choice after?
Or is it just try and plough through it all in the time

Cheers
16. (Original post by Ayaz789)
The right one is more positve but idk how to sketch it?
Like this. Sorry its in landscape.

17. (Original post by SirRaza97)
Like this. Sorry its in landscape.

I thought like charges repel?
18. How do you do this?
19. (Original post by Nikhilm)
Your first point is right. The forces are inwards and along the same line of action. Hence they cause no torque
How are the forces not a couple then? if they are pointing towards one another they are two equal in magnitude forces that oppose one another....isnt that a couple?
20. (Original post by xMillnsy)
How do you do this?
Find the speed at which the water moves

speed is equivalent to a length per second, so speed = volume / area

mass = density x volume

momentum = mass x velocity

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