Offcial Physics A thread for the G484 Jan Exam (Newtonian World)

Hey guys I am aware this is very early! But Physics requires practice , have you guys started this module yet?

Thoughts on it? Personally i think its really interesting
How did you guys do in AS? etc

Good luck guys and shaare knowledge!

Specification
http://pdf.ocr.org.uk/download/kd/oc..._gce_spec.pdf?

Past Papers
http://www.ocr.org.uk/qualifications...s_a/documents/

From Jan 10 to Jan 12 with mark schemes - http://www.mediafire.com/?omrcsu4pef8tobe

Older Paper Questions (good for practice if you've gone through all the current spec papers):

Circular Motion & Simple Harmonic Motion - http://www.mediafire.com/?n8u8vcibmfbl7l4

Thermal Physics - http://www.mediafire.com/?39wnyg73q1w93jn

Revision Websites
http://www.st-ambrosecollege.org.uk/...sics-a2-level/

Powerpoint Presentations & Worksheets
http://www.mediafire.com/?4g9ahc4kj707nui
http://www.mediafire.com/?39wnyg73q1w93jn

You might want to change the thread title to clarify that you are talking about the 'A' syllabus. Also, the OCR website has changed its URLs so your links are broken (the ones to OCR I mean).

Oooh yes, shall i put thatup on the first post if you don't mind?

Also did you just put up the ''motion'' questions up? (i.e would they be relevant to G484?)

G485 is interesting, but there's a LOT of different stuff to remember - most of the content doesn't really tie in with other parts of the module

G484 is okay, make sure you understand all the content as you do it in your lessons. Then when it comes to the exams all you have to do is memorise all the definitions and practice exam technique, leaves you with a LOT less work to do

We are studying about gravitational field strength and i havea few questions... why is the gravitational field strength of earth uniform over short distances? ALSO I can't find an answer to ''Describe how a mass creates a gravitational field in the space around it.

THANKS!

As you approach the surface of the earth, it's curvature is almost negligible - therefore for all intents and purposes it's 'flat'. This means that the field lines are parallel and not getting any closer to each other, meaning that the field strength is uniform.

It's a describe (not an explain! different type of question altogether) question so you just have to talk above the law of gravitation, the fact that it's a radial field, the fact that it's an attractive force and point masses move towards it. Maybe some other stuff too but you get the general idea as no-one understands exactly how gravity works

Thanks!! You make a good physics teacher , in the future am i allowed to quote you with more questions?

yeah, sure

it's a while since I did G484 though

Yaay, so hopefully you could help me with two questions, if it isn't too much trouble! Okay:
1) Why can gravitational field lines never cross?
Becauseif an object was placed in a certain point where the fields cross then in turn it would mean that the object will accelerate in 2 different directions, which is not allowed.. <-- is this right?

2)How far above the surface of the Earth is the gravitational field strength (a) half and (b) one quarter of its value at the surface? The radius of the Earth is 6.4x10^6 m.

I know you use the inverese square law, but i really can't get my hear around proportionality! and when i google proportionality it comes up with KS3 stuf... :/ So yeah could you explain please? Thanks!

1) Correct - plus the field lines are vectors and they add up/subtract

2) You know the field strength g = GM/(r^2)

so g is proportional to 1/(r^2) - find the constant of proportionality and substitute the values of g into there (g/2 and g/4) to find out the radius.

Thanks, how does the fact that vectors which add and subtract add to the answer?


I'm sorry for being stupid, but I didn't know that formula. Also, i have no idea how to do proportionality! what is the constant of pptt? is that K? And how do i find it out?

Well the field lines could be combined in to one field line

Field lines never cross. (If they did, then an object placed at the point where they crossed would feel forces in more than one direction. These forces could be resolved into one direction – the true direction of the field line there.)
http://tap.iop.org/fields/gravitational/page_40076.html

Basically, for proportionality, if you have a formula and you know that some of the variables don't change, you can 'merge' these variables into one constant, the constant of proportionality, while keeping the formula the same.

In the formula I showed you, G (the gravitational constant) and M (the mass of the earth) are both constant.

The constant of pptt is K - use the values that you already know (g = 9.81, and the known radius of the earth at it's surface) to find it out.

$g = \frac {k}{r^2}$

Thanks for all the effort, 1) if the forces could be resolved into one direction to find out the true direction of the field line, then surely it wouldn't matter?

And after i find K which is 6278400, what do i do?

strictly no, but as a result you can't have 2 intersecting field lines

and rearrange the equation by solving for r, by putting in the various values of g.

Could you expand a bit? on first bit? (I bet i am driving you up the wall)soo sorry..

They'd 'add' up if you had two separate field lines to form one overall

And i'm guessinng we do not want that.. So in tuurn spacing is important when drawing field lines as well.
For the calculation i got 3578 and 5060m do they seem reasonable?



I think i finallyy got it! Unless the second bit is wrong...

Errr, have you got that right? If the radius is 6.4x10^6m and it's an inverse square law you should have got a value greater than that of the radius

I'd have a look but I don't have a calculator handy and I'm on my phone

Errr, have you got that right? If the radius is 6.4x10^6m and it's an inverse square law you should have got a value greater than that of the radius

I'd have a look but I don't have a calculator handy and I'm on my phone