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

1. (Original post by DanTheMan358)
2mJ is the correct answer to the question
4mJ is the correct energy of the battery
2. Ok this was probably the easiest paper to of come up

having said that its the paper I ****ed up in the most

good bye firm choice
3. Guys, let me know if you got the same answers

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4. Newton's first law at the end i put because no force in direction of velocity (always tangential) it remains at constant speed. Is that ok for the first law
5. (Original post by TheRAG)
what did y'all put for the six marker?

There is always a centripetal force acting towards the centre greater than zero so the mass always accelerates towards the centre.
There is a gravitational force acting on the mass (mg). This means the string has to subtend an angle theta < 90 degrees in order to ensure there's a vertical component of centripetal force in order to oppose the weight of the mass. This means the string in practice is never horizontal. Centripetal force always acts at right angles to the motion so F=0 in the direction of motion this means there is no acceleration in the direction of motion and hence the speed of the mass remains constant throughout revolutions
6. (Original post by NEWT0N)
I read what you said and I disagree: for damping to occur it is only necessary for the amplitude must be affected. Damping forces reduce amplitude, not time period.
Oh dear then
7. For flux linkage i put Tm(squared) ? is that ok?

Also what did people put for the distance between the surfaces of the 2 spheres mass M radius R when F/9?

2R, 4R, 8R or 12R?
8. (Original post by AR_95)
Ok this was probably the easiest paper to of come up

having said that its the paper I ****ed up in the most

good bye firm choice
Welcome 2 the club
9. What did people put for the forced vibrations?

I remember using the cgp explanation: A system can be forced to vibrate by an external periodic force called the driving force. If the driving force does not have the same natural frequency as the system, the amplitude of oscillation will be smaller than that in free vibration.
10. (Original post by crs96)
For flux linkage i put Tm(squared) ? is that ok?

Also what did people put for the distance between the surfaces of the 2 spheres mass M radius R when F/9?

2R, 4R, 8R or 12R?
I said 2R ??
11. (Original post by NEWT0N)
It's just lenz's law. A flux moving in the opposite direction causes the coil to set up a field in the opposite direction to the flux. Initially it sets up a field opposite to a flux moving in direction X (say), then it sets up a field in the opposite direction to -X. X is opposite to -X so the induced current the second time round is opposite.
The only thing that changed was an increase in resistance. They didn't reverse the direction of the current. So why would a field be produced in the opposite direction?
12. (Original post by NEWT0N)
What did people put for the forced vibrations?

I remember using the cgp explanation: A system can be forced to vibrate by an external periodic force called the driving force. If the driving force does not have the same natural frequency as the system, the amplitude of oscillation will be smaller than that in free vibration.
Yeah I said that but quoted phase differences
13. (Original post by Mehrdad jafari)
Guys, let me know if you got the same answers

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I think your acc graph is wrong (not sure). The distance between planets is definitely 4R as initially F is proportional to 1/4R^2 then it becomes 1/9 F so 4*9=36 root36=6 then 6-2=4 (as it says between planets so u remove each radi)
14. (Original post by louisg565)
Do you think Ill get the mark for flux linkage unit if I just put 'Wturns'?

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Hope so but probably not..
I did the exact same ffs.
15. (Original post by crs96)
For flux linkage i put Tm(squared) ? is that ok?

Also what did people put for the distance between the surfaces of the 2 spheres mass M radius R when F/9?

2R, 4R, 8R or 12R?
4R

(Original post by SuperMushroom)
Welcome 2 the club
Surely that is the funniest Emoji?
16. I don't think i have done as well as i had hoped. What do you guys think the grade boundaries will be?
17. (Original post by chizz1889)
I think your acc graph is wrong (not sure). The distance between planets is definitely 4R as initially F is proportional to 1/4R^2 then it becomes 1/9 F so 4*9=36 root36=6 then 6-2=4 (as it says between planets so u remove each radi)
His graph is correct
18. Goodbye firm choice, it was nice thinking it was possible to be there but now my dreams have been smashed! Never seen so many word answers in a physics test before!!

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19. (Original post by chizz1889)
I think your acc graph is wrong (not sure). The distance between planets is definitely 4R as initially F is proportional to 1/4R^2 then it becomes 1/9 F so 4*9=36 root36=6 then 6-2=4 (as it says between planets so u remove each radi)
Yes I also got 4R. Was confused at first but went back to it with a few mins to go and it was all so clear the fact that the seperation when they were touching was 2R made it sort of confusing
20. I thought that paper wasn't one of the easiest but defo easier than last year. I only had to guess 2 multi choices and they where estimates I felt confident in every question they asked and especially the change in the height thing for the capacitor! Absolute babe of a question! Thanks for all the help everyone's given me and good luck on results day! Going to imagine I've completely failed this now and get straight on with unit 5, see you on the other side (unit 5 forums)

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