AQA Physics PHYA4 - Thursday 11th June 2015 [Exam Discussion Thread]

ah, so is Resultant Force (R) the opposite of T? ie the negative form of those equations is R?

Oh sorry, I mistook your (R) to mean the reaction force.

The resultant force is the centripetal force, and is always directed towards the centre of the circle.

The centripetal force IS the resistance force, and as such there's not a PHYSICAL force labelled as the "centripetal force". It is more a case of the centripetal/resultant force being the net effect of all other forces acting on the body to keep it moving in a circular path.

In vertical circles, for example on a fairground Ferris wheel, generally the upwards and downwards forces are the normal reaction force (labelled N or R) and the weight (mg - which always acts vertically downwards).

At the top, the reaction force acts upwards and the weight acts downwards, so the resultant force, mv^2/r = mg - N because the weight is pointing towards the centre of the circle.

At the bottom the reaction force still acts upwards and the weight acts downwards, but this time the reaction force acts upwards towards the centre, so the resultant force, mv^2/r = N - mg because the reaction is pointing towards the centre of the circle.


Does this make sense?




Posted from TSR Mobile

Wow you really know your physics! thanks so much, that makes much more sense.
The question that had me stuck in the first place was June 2011 1)aii on section B where it asked to write and equation relating contact force, R, with mvrg for a parcel on the floor of a van travelling over the highest point of a bridge. So that would be the force acting upwards right? Hence the equation would be mg-mv^2/r ?

Unit 4 isn't that bad actually, it's the empa that's worrying

Looking at past papers, with similar tasks. Also looking at uncertainties, errors etc

Cool, will have a look in a bit.

Sure. Good luck for the 7th.


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Good luck to you to!

Posted from TSR Mobile

When is your practical?

Just relax and take a look through the Nelson Thornes AQA textbook if you have it. It's useful for both sections


Posted from TSR Mobile

Thanks. I'll take your advice. My second practical test is next tuesday.

Oh nice! Do you know when your section B is? Mine is on 5th May


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Mine is on 7th May.

could you possibly upload a link to the unit 5 paper and mark scheme? Thanks

Let's say I get U for my overall practical test. What grade must I need to get for written test to obtain B, C, or D grade overall? I need to get B overall for physics to get into ediburgh university, but it seems like my chance is slim.😔 I'm going to retake all physics units this summer.


Posted from TSR Mobile

It's hard to say overall without knowing last year's results, but based on this year, it's 210/300 for a B, 180/300 for a C and 150/300 for a D.

This practical unit is worth 60 UMS, so it's perfectly feasible for you to get enough UMS in both theory papers to amount to those grades for this year overall, but it's hard for me to understand what that would be overall without knowing last year's results.


Posted from TSR Mobile

Thanks for this useful information. Frankly speaking, I got U for unit 3 empa last year and C for unit 2. However, I'm going to retake them. So basically, I'm going to sit the whole physics exams this year.