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

1. To be honest there is no point discussing the written one. It all comes down to what examiners think is right

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2. (Original post by chizz1889)
Less damping, mass is increased and so therefore is momentum. Increased momentum results in resistive forces having a lesser effect on the motion of the pendulum, thus less damping.
Think this is incorrect. The time period of a pendulum is independent of a mass added, hence the maximum velocity is independent of the mass added. Furthermore, the only resistive force is due to the viscosity of air, an air resistive force. The ring hardly affects air resistance, and so the since the vicious force of air is dependant on velocity, which is unchanged, then the damping/viscous force is unchanged.

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3. for the emf question in section B was it just change in flux linkage over the time or was it rotating contiously? cant remember the question
4. (Original post by Mehrdad jafari)
Guys, let me know if you got the same answers

Attachment 425441

Q.22 is 1/√2
I got 21 wrong (I put A)

All other answers SAME! Weeeeeeee
5. (Original post by QueNNch)
Q.22 is 1/√2
All other answers SAME! Weeeeeeee

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Yeah, i think i got that wrong.

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6. On the 6 marker, I said that the string may not remain horizontal because of the frictional force of air which acts against the mass, lowering its Ke and velocity. Is that even remotely close to any mark
7. (Original post by Alexie56)
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?
I thought this, so I said that the needle lowers i.e. a lower value of current
8. (Original post by Amanzz)
Think this is incorrect. The time period of a pendulum is independent of a mass added, hence the maximum velocity is independent of the mass added. Furthermore, the only resistive force is due to the viscosity of air, an air resistive force. The ring hardly affects air resistance, and so the since the vicious force of air is dependant on velocity, which is unchanged, then the damping/viscous force is unchanged.

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Definitely not incorrect, I got it incorrect I said no damping. Change in Damping is not how to air resistance varies. It his how the air resistance varies in relation to change in momentum. If you don't believe me go and do an experiment, damping has no effect on time period in the first place.
9. (Original post by AR_95)
I mentioned the velocity is constantly changing because of the centrapetal force
I did the same.

(Original post by NEWT0N)
Yes because a force is impressed on it. When there is no longer a force it is constant throughout its motion from release and follows a parabolic curve. The horizontal velocity now remains the same as the tangential velocity at the point of release, in accordance with Newton I.
So just to confirm; by stating the *ball it's constantly accelerating, you confirm there must be a resultant force acting on the ball while it is traveling in a circle (law 1); and relating this to F=ma is law 2?
10. (Original post by rohan9777)
for the emf question in section B was it just change in flux linkage over the time or was it rotating contiously? cant remember the question
You're correct, change in flux linkage over time, Faraday's law of induction.

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11. (Original post by AR_95)
On the 6 marker, I said that the string may not remain horizontal because of the frictional force of air which acts against the mass, lowering its Ke and velocity. Is that even remotely close to any mark
I said the compinent of the weight (mg) wasnt taken into account, this component acts downwards and would bring it out of the horizontal
12. NEED to get an A in physics for any uni and may have just ended it today :/.
Section A I didn't think was too bad, rushed but hopefully mostly ok.
Section B though.. omg.. it was all stuff I hate and wordy. Even on the numbers that I'm good at I rushed and got a lot of it wrong.
Then the capacitor question I got completely confused by due to the 300K ohm resistor, didnt think they would want me to draw a line on the bottom of the graph so started it at the same current and made the gradient shallower with the same shape (i know I should have started below the initial current).
No gravitational questions either to get my mark back up .
13. (Original post by rohan9777)
for the emf question in section B was it just change in flux linkage over the time or was it rotating contiously? cant remember the question
It was rotating so you had to use BANwSinwt then divide by root2
14. (Original post by Amanzz)
You're correct, change in flux linkage over time, Faraday's law of induction.

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I got something like 0.12?
15. Why were there 50 answer boxes for the multiple choice?
16. (Original post by NEWT0N)
I remember getting G*m*pi*p*R/3 somewhere for the multiple choice. Anyone agree?
Yes!
17. Section B Q2

What did you all say for why V is negative on the graph?
18. (Original post by NEWT0N)
Why were there 50 answer boxes for the multiple choice?
I think that is a general sheet for AQA exams and not specifically for phys4

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19. Well I finally got home! Seemed an average paper, pretty sure I've done well enough for an A* but won't know for sure until August. I'd expect pretty normal grade boundaries, something along the lines of the last few years.
20. (Original post by Disney0702)
Section B Q2

What did you all say for why V is negative on the graph?
The charge was negative and so negative potentials are associated with a negative charge

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