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

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Reply 3480

a.a.k

Original post by Plasmapause

Could someone explain why question 1 of this paper is C?

Ft=mv

So v =Ft/m

(0.5*10*40)/0.25=800

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Reply 3481

RemainSilent

Original post by Kennethm

do you know what situation will mean that M/x² = - 4M/y²

^{Sometimes I cant tell when the minus matters. It might only be for potential.}

If it says potential is zero and one of the charges on negative would you need to include the negative or not? SOmetimes they do sometimes not (although I think they do)

Reply 3482

Boop.

Original post by SilenceOrNoise

Because the magnetic field lines are not passing through the charged particles at RIGHT ANGLES. Therefore, the magnetic force would not act where the particles would move unaffected.

Thanks, got mixed up with electric fields

Reply 3483

Kennethm

Original post by RemainSilent

If it says potential is zero and one of the charges on negative would you need to include the negative or not? SOmetimes they do sometimes not (although I think they do)

ive been trying to find out lol

https://60abffc9b401b1c0936e01291c15112cab0778c4.googledrive.com/host/0B1ZiqBksUHNYVFI1YlJBOWhwRW8/June%202010%20QP%20-%20Unit%204A%20AQA%20Physics.pdf

Q13, the answer is A meaning you dont make it minus on the other side. Which makes me wonder do you do the same or the opposite if they were positive?

Reply 3484

HenryHein

Original post by Kennethm

do you know what situation will mean that M/x² = - 4M/y²

^{Sometimes I cant tell when the minus matters. It might only be for potential.}

Never would be the case as gravity is always attractive and hence the force exerted on a point mass by other masses will always have the same sign.

In gravitational fields a minus is used for potential. The idea is that being in a field is like being in an "energy well" and energy must be done to be in a "neutral state" (i.e. out of the field) in the same way electron energy levels are given negative values.

Reply 3485

Patar31

Anyone got any ideas what the QWC will be on?

Reply 3486

a.a.k

Original post by Patar31

Anyone got any ideas what the QWC will be on?

I think it would be on comparing electric filds magnetic fields and gravitational fields

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Reply 3487

Plasmapause

Original post by a.a.k

Ft=mv

So v =Ft/m

(0.5*10*40)/0.25=800

Posted from TSR Mobile

Thanks for the reply.
Just wondering but where did the 0.5 come from? :confused:

Reply 3488

oonic0rn

anyone know why when doing ratio multiple choice and this like that you dont take into account the square root??

Reply 3489

a.a.k

Original post by Plasmapause

Thanks for the reply.
Just wondering but where did the 0.5 come from? :confused:

Aeea under the graph.
Sorry didnt made that clear before.

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Reply 3490

oonic0rn

predictions for 6 marker? :tongue:

Reply 3491

HenryHein

Original post by lukebiddell

I get it now thanks! Goodluck tomorrow

and you

Reply 3492

SuperMushroom

How do you answer question 25 on this please!

http://filestore.aqa.org.uk/subjects/AQA-PHYA41-QP-JUN14.PDF

Reply 3493

IWantSomeMushu

Anyone else here planning on doing Section B first?

Reply 3494

dominicwild

How do you answer this question?

Reply 3495

RemainSilent

Original post by Kennethm

basically im at the stage at:
either:
1) 480-4x = -16x
2/ 480 - 4x = 16x

for 1 the answer would be negative 20 positive (right one i think)

I have had an idea maybe because potential is scalar you can ignore negative? (seems like an excuse tho :tongue:

)

Reply 3496

HenryHein

Original post by SuperMushroom

How do you answer question 25 on this please!

http://filestore.aqa.org.uk/subjects/AQA-PHYA41-QP-JUN14.PDF

Primary power= 0.26*230 = 59.8W

Secondary voltage:

As Ns/Np = Vs/Vp,
Vs = Vp * turns ratio
= 230 * 500/1150
= 100V

Secondary power= 100V*0.5A= 50W

50/59.8 * 100 = 83.6% so C

Reply 3497

RemainSilent

Original post by dominicwild

How do you answer this question?

is the answer A?

Reply 3498

Deddy

Original post by oonic0rn

http://filestore.aqa.org.uk/subjects/AQA-PHYA4-1-QP-JAN13.PDF -

could someone please explain number 9 :smile:

and 10 please

9) The phase difference between P and Q is 0.05s, it takes Q 38 oscillations to move in phase with P as with every oscillation it is doing is 0.05s slower. 1.9/0.05 =38.

10) The forces between M1 and the small mass is equal to the force between M2 and the small mass. If you call the small mass m, GM1m/r1^2 =GM2m/r2^2 , the m will cancel, then you rearrange to get answer C. :smile:

Reply 3499

SuperMushroom

Original post by HenryHein

Primary power= 0.26*230 = 59.8W

Secondary voltage:

As Ns/Np = Vs/Vp,
Vs = Vp * turns ratio
= 230 * 500/1150
= 100V

Secondary power= 100V*0.5A= 50W

50/59.8 * 100 = 83.6% so C

Thanks mate!

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

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