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

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1. Can anyone explain why kinetic energy = 1/2 potential energy for satellites in orbit?
2. (Original post by wallpaperpaste)

Can anyone explain why kinetic energy = 1/2 potential energy for satellites in orbit?
This should help
3. (Original post by Nathanbh321)

This should help
Yes I derived it the same way as you did but I couldn't come up with a proper qualitative explanation for it so I hoped someone might know
4. (Original post by wallpaperpaste)
Yes I derived it the same way as you did but I couldn't come up with a proper qualitative explanation for it so I hoped someone might know
Why are electrons negative? I think it's just a quirk of nature but the formulae show you that has to be the case
5. (Original post by Nathanbh321)
Why are electrons negative? I think it's just a quirk of nature but the formulae show you that has to be the case
I think it's just a quark of nature
6. would anyone please be able to explain to me why the answer to question 5(a)(i), in the June 2013 paper, is 60 degrees?
7. (Original post by veldt127)
I think it's just a quark of nature
I appreciate the pun but electrons are leptons and not quarks. So can we please stick to scientifically correct puns
8. (Original post by cowie)
would anyone please be able to explain to me why the answer to question 5(a)(i), in the June 2013 paper, is 60 degrees?
EMF is max when the coil is parallel to the field lines therefore the coil must be rotated 60 degrees to be parallel
9. (Original post by Nathanbh321)
I appreciate the pun but electrons are leptons and not quarks. So can we please stick to scientifically correct puns
I know
I couldn't resist ohmitting that pun, sorry.
10. Need help with a question on this page if anyone can provide their input that would be great.

http://www.antonine-education.co.uk/...ag_field_7.htm

Question 4 at the bottom, part b. Do we multiply the output current by 1.05 (due to transformer being 95% efficient) to give 42kA? Giving the answer of 318A. Or do we simply use the 40kA and get an answer of 303A.
11. 6 marker predictions anyone?
12. anyone else panicking at this point?
13. (Original post by Brailey)
EMF is max when the coil is parallel to the field lines therefore the coil must be rotated 60 degrees to be parallel
This has confused me,

E=BAN/t

If it is rotated 60 degrees, BANcos(theta) becomes 0 at 90degrees so why doesnt that make E 0?
14. (Original post by wallpaperpaste)

Can anyone explain why kinetic energy = 1/2 potential energy for satellites in orbit?
We now that Force on an object can be shown as F = mv^2/r = GMm/r^2. This force can be related to the kinetic energy of the object by EK = 0.5Fr =0.5mv^2 which is obviously in Joules(J).
As mv^2/r =GMm/r^2 we can show that EK = 0.5mv^2 = 0.5GMm/r.
Gravitational Potential of a body is given as V =-GM/r which is in Joules per Kilogram(JKg^-1) however, you need the work done to move the object from infinity to a point in the field which is given as W = m x change in gravitational potential which is in Joules(J). So it's not actually the gravitational potential that is relevant to potential energy but the Work needed to move the object of mass m from infinity to a point in the field.
So now we can write W as W = EP = -GMm/r, and as EK =0.5GMm/r we can simply say that EK=-0.5EP.

I hope this helps and didn't sound too patronising, I'm not the biggest fan of worded explanations.
15. (Original post by Throor)
anyone else panicking at this point?
With the way my other exams have been going, I'm so worried
16. (Original post by ManOfJustTin)
With the way my other exams have been going, I'm so worried
Don't worry, it'll only have an impact on the rest of your life
17. (Original post by veldt127)
Don't worry, it'll only have an impact on the rest of your life
Thanks buddy
18. (Original post by ManOfJustTin)
With the way my other exams have been going, I'm so worried
19. (Original post by ManOfJustTin)
Thanks buddy
On a serious note, there isn't much you can change now, so focus on getting enough sleep. Maybe get up earlier than usual and do some work beforehand, I find that more helpful than working the night before.
20. (Original post by aksdj)
For Physics, I just need an A but it would be nice to try and get the A*

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