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

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Reply 620

WillRose

You're thinking of geo-synchronous satellites, if you go from -60 to -20 you've gained +40 potential

Reply 621

1017bsquad

Original post by kingaaran

Why is it wrong - you will get the marks if you write 2.7, the brackets are to show examiners what the other significant figure needs to be to ensure candidates have used a valid method.

In response to your second question, they've used the atomic mass unit, not the mass of the proton which is of course correct - on their formula booklet they clearly say u=1.661 x10^(-27)

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Hey do you mind helping me on this question, I know that T^2 is proportional to m/K, but I do not know how to go about this, thanks in advance!

Reply 622

duncant

can anyone tell me why the paper is in this style?
http://filestore.aqa.org.uk/subjects/AQA-PHYA4-1-QP-MEP18-JUN13.PDF

it has the same q's as the official june 2013 paper, but it says it modified? its on the official aqa website. just curious as to what it is.

Reply 623

micycle

Original post by Charlie1523

Can anyone help with this? thanks http://filestore.aqa.org.uk/subjects/AQA-PHYA41-QP-JUN13.PDF
Question 19

Field lines are going from left to right which indicates the point charge is negative.

With this in mind:

Cannot be A: Electric force would increase as the negative ion comes closer to the negative charge.
Cannot be B: Potential energy is inversely related to r. To the right, r would increase and reduce the potential.
Cannot be C: It stays at the same radius so potential energy is constant.

So its D.

Reply 624

WillRose

Original post by philo-jitsu

Okay so pretty good with mosr areas now....the only thing im struggling wkth is potentials.

For both grav and electric potentials do two masses or charges interact with each other.....for instance is you were 500km above earths surface and there was no moon your potenital=x ....now if the moon is there what happens to the potential at the same spot?

you'd gain potential, grav potential is scalar not vector

edit: i'v had a think about it and confused myself

(edited 7 years ago)

Reply 625

MintyMilk

Original post by ssel17

SOMEBODY PLEASE HELP ME WITH THIS - Cannot get my head around it at all.

Two satellites P and Q, of equal mass, orbit the Earth at radii R and 2R respectively.Which one of the following statements is correct?
A P has less kinetic energy and more potential energy than Q.
B P has less kinetic energy and less potential energy than Q.
C P has more kinetic energy and less potential energy than Q.
D P has more kinetic energy and more potential energy than Q.

My issue here is surely Q, travelling at a higher radius than P, would have a higher speed and hence more kinetic energy? But that's wrong according to the answer. Also, doesn't the potential decrease at increased distance, or are we including because its minus???

It says potential energy, which is affected according to mgh, so it increases as you increase the distance.

I can just about explain the kinetic energy, I mean I think the explanation is valid: higher R means lower angular velocity, lower angular velocity means lower linear velocity, thus a smaller R means higher linear velocity?

This would be much simpler if we were told they both have the same angular velocity, or just something like that to use, otherwise I just feel like I'm just fiddling the 3 variables to produce the outcome I want without considering the actual Physics

(edited 7 years ago)

Reply 626

alevelstresss

if anyone wants, here are my PHYA4 notes :smile:

PHYA4 - notes REVIEW.docx97.6KB

Reply 627

Charlie1523

Original post by micycle

Thank you so much! if its not too much to ask would you mind looking at question 23 for me aswell, thanks again :smile:

Reply 628

ssel17

Original post by alevelstresss

No, the satellites which orbit closer have higher speed and therefore kinetic energy

Think of it as the further out the satellites are, the higher their potential energy and therefore the lower their kinetic energy

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.

Reply 629

alevelstresss

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.

Think of kinetic energy and gravitational potential energy as interchangeable.

Satellites which orbit far out have very high GPE, and must therefore have lower KE.
Satellites which orbit close have very low GPE, and therefore must have higher KE.

The satellites orbiting far out travel a greater distance, as d = 2 x pi x radius

Reply 630

ssel17

Original post by alevelstresss

Okay, thank you. I think my main issue here is because we are not told whether they have the same time period, I feel we're lacking information to answer the question.

Reply 631

Brailey

Original post by duncant

I Believe its the visually impaired version

Reply 632

micycle

Original post by Charlie1523

Thank you so much! if its not too much to ask would you mind looking at question 23 for me aswell, thanks again :smile:

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

Therefore it's A.

Reply 633

ssel17

Original post by WillRose

You're thinking of geo-synchronous satellites, if you go from -60 to -20 you've gained +40 potential

Yeah I sort of get that, I always have a bit of an issue with it because even though it of course is a higher potential, you've lost magnitude, if that makes sense? I struggle to know which they are asking for.