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

1. (Original post by alevelstresss)

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2. (Original post by ssel17)
Well looking at the answer tells me that, but why? I don't understand how with a lower radius, they travel at a higher speed.
Orbiting occurs when GMm/r^2=mv^2/r

rearrange and GM/r=V^2 hence V^2 is inversely proportional to radius.

In terms of a worded explanation I think its down to the gravitational force increasing as the radius decreases. So apply this to centripetal force, the mass is constant and radius is decreasing and F=mV^2/r so if r is decreasing and F is increasing and mass is constant velocity must increase in order for centripetal to equal gravitational force.

I dont think this applies to a charge in a magnetic field though.....and I dont know why...how does range affect magnetic field?...its not an inverse square law?
3. Here are my physics unit 4 notes hope they are useful to anyone revising

https://www.dropbox.com/s/s4zgakd11h...VIEW.docx?dl=0
4. tips for 6 marker questions anybody? :\
5. (Original post by philo-jitsu)
Orbiting occurs when GMm/r^2=mv^2/r

rearrange and GM/r=V^2 hence V^2 is inversely proportional to radius.

In terms of a worded explanation I think its down to the gravitational force increasing as the radius decreases. So apply this to centripetal force, the mass is constant and radius is decreasing and F=mV^2/r so if r is decreasing and F is increasing and mass is constant velocity must increase in order for centripetal to equal gravitational force.

I dont think this applies to a charge in a magnetic field though.....and I dont know why...how does range affect magnetic field?...its not an inverse square law?
Ahh! That finally makes a lot of sense if you put it like that! Thank you
6. (Original post by micycle)

There isn't a couple because the forces oppose each other.

Therefore it's A.
surely if they oppose each other it will cause a couple :s
7. (Original post by philo-jitsu)
In terms of a worded explanation I think its down to the gravitational force increasing as the radius decreases.
gah, it was so simple all along
8. (Original post by blueberry389)
tips for 6 marker questions anybody? :\
Write in a coherent manner and use paragraphs ect, then at least if your physics is bad you'll get QWC marks
9. (Original post by WillRose)
surely if they oppose each other it will cause a couple :s
In a couple they need to going in the same direction (as in clockwise or anti-clockwise). In this question the force from one is clockwise and the other one is anticlockwise.
10. (Original post by duncant)
for 11, you are using the wrong formula. when it asks about potential energy, think graviatational potential. If you jump, you gain gravitational potential, and as you fall you loose that graviational potential. The field lines point towards, for example, the centre of the earth. thus A is right. B and C are correct, so D is wrong. and it you look at the formula, g=GM/r^2 so it is actually inversely proportional to r^2.

10 is B as the pattern for damping is B and D, and light damping does not reduce the amplitude greatly, thus the amplitude is higher than D, so B.
Oh ok, you make it seem so obvious, really well explained, thanks!

Where you said to think about gravitational potential, A says potential energy, so how did you know to use gravitational potential? Also even using gravitiational potential, isnt it still inversely proportional to r aswell?

Thanks a lot
11. (Original post by micycle)
In a couple they need to going in the same direction (as in clockwise or anti-clockwise). In this question the force from one is clockwise and the other one is anticlockwise.
thanks yeah, just realised which way the forces are going
12. anyone thinking a SHM 6 marker might come up??
13. (Original post by alevelstresss)
anyone thinking a SHM 6 marker might come up??
hopefully something about resonance, got all that down to a t
14. anyone got any ideas about how two masses affect the potential of a point in a field, for example if 500M from earth the potential = x, if we then placed another earth on the opposite side but equal distance away, what would the new potential be 500M from both earths? zero or 2X???!!

this i pretty much the only thing I cant wrap my head around...Im trying to find an example question
15. Any hard/novel ideas anyone has come across from non-AQA past papers?
16. (Original post by micycle)

There isn't a couple because the forces oppose each other.

Therefore it's A.
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
17. (Original post by WillRose)
hopefully something about resonance, got all that down to a t
Highly doubt it, resonance partly came up last year + mechanics 6 marker last year
18. http://filestore.aqa.org.uk/subjects...2-QP-JAN13.PDF
How would i do 4bi?
19. (Original post by philo-jitsu)
Orbiting occurs when GMm/r^2=mv^2/r

rearrange and GM/r=V^2 hence V^2 is inversely proportional to radius.

In terms of a worded explanation I think its down to the gravitational force increasing as the radius decreases. So apply this to centripetal force, the mass is constant and radius is decreasing and F=mV^2/r so if r is decreasing and F is increasing and mass is constant velocity must increase in order for centripetal to equal gravitational force.

I dont think this applies to a charge in a magnetic field though.....and I dont know why...how does range affect magnetic field?...its not an inverse square law?
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
20. 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.

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