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

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Reply 780

wallpaperpaste

Can anyone explain why kinetic energy = 1/2 potential energy for satellites in orbit?

Reply 781

Nathanbh321

Original post by wallpaperpaste

Can anyone explain why kinetic energy = 1/2 potential energy for satellites in orbit?

This should help

Reply 782

wallpaperpaste

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

Reply 783

Nathanbh321

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

Reply 784

veldt127

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

Reply 785

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?

Reply 786

Nathanbh321

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

Reply 787

Brailey

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

Reply 788

veldt127

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.

Reply 789

slb971

Need help with a question on this page if anyone can provide their input that would be great.

http://www.antonine-education.co.uk/Pages/Physics_4/Magnetism/MAG_07/Mag_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.

Reply 790

TJ_gym

6 marker predictions anyone?

Reply 791

Throor

anyone else panicking at this point?

Reply 792

particlestudent

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?

Reply 793

davies_

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.

Reply 794

ManOfJustTin

Original post by Throor

anyone else panicking at this point?

With the way my other exams have been going, I'm so worried :frown:

Reply 795

veldt127

Original post by ManOfJustTin

With the way my other exams have been going, I'm so worried :frown:

Don't worry, it'll only have an impact on the rest of your life

Reply 796

ManOfJustTin

Original post by veldt127

Don't worry, it'll only have an impact on the rest of your life

Thanks buddy :h:

Reply 797

aksdj

Original post by ManOfJustTin

With the way my other exams have been going, I'm so worried :frown:

what grades do u need

Reply 798

veldt127

Original post by ManOfJustTin

Thanks buddy :h:

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.