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

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    (Original post by Mehrdad jafari)
    Yeah, that would make it exact


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    What about question 13 on that paper. I can't seem to get it


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    (Original post by bwr19)
    If you're reading off a graph then technically you shouldn't quote it to any more precision than the scale itself. So, if each grid line was 0.1, you could only answer with 1d.p.
    I'm not talking about specifically about dp just when the value is not the one shown. Like if for example in the answer to the first part (image) I put lnVo = 2.13 (reading from a graph) instead of 2.15. Would I get follow-on marks?
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    (Original post by gcsestuff)
    What about question 13 on that paper. I can't seem to get it


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    I think again it is m/r^2

    *sorry for bad quality
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    (Original post by CD223)
    In recent years they've bullet pointed exactly what we have to say.

    With circular motion they could give us an application such as a vertical circle and we would describe how the centripetal force changes in terms of what makes it up (T-mg or mg-T etc) and things like whether work is done/what does and doesn't change and the direction of the velocity/displacement/acceleration in relation to the motion.

    SHM could be an experiment with a pendulum or mass spring system like the EMPA.


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    Just a thought- shm could be about a bridge with people walking on it at the bridges natural frequency?

    Can't recall seeing a question like this on the newer papers


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    (Original post by Lau14)
    I'll admit I guessed (and got it wrong!) first time round.
    But you're looking at M/r^2 (as the mass of the satellite is the same for all of them, and G is a constant). You can assume distance from Earth to Moon and Earth to Sun to be the same as satellite to Moon and Sun, as it's in low orbit. Calculate M/r^2 for the moon and sun - the sun's is biggest so FS > FM. Then it's so close to the Earth that the Earth's must be largest (or Earth's must be largest for circular motion to happen, otherwise it would be pulled away I think?).
    (Original post by Mehrdad jafari)
    That question is very intuitive. I think it would better to think about it logically than mathematically, in terms of what's causing the orbits in the first place. So if the space shuttle is in orbit, it's in orbit around the earth "first". Then the earth along with the space shuttle are in orbit around the sun and then along with the moon. Therefore the force exerted by the earth should be greater ( because if the space shuttle were not to orbit it would fall towards the earth and not towards the moon or the sun). Then the force exerted by the sun should be next because the earth and the space shuttle are both in orbit around the sun( because if the earth were not to orbit it would fall, along with the space shuttle, towards the sun). And then moon comes last because moon is in orbit itself around the earth
    (Original post by Adangu)
    i just thought realistically what would it be and picked A.

    My teacher went and worked it out and it was A.

    So could you use g=GM/r^2 ?
    and then F=mg?

    Sorry i have no clue, I just used common sense really, although not reliable it did save me a lot of time when doing the paper as 1-2 minutes is a lot when you think about it!
    I see thank you everyone!

    What confused me is the maths and logic seemed to contradict each other! I'll try and redo the question another time and see if I get the correct answer.

    Would you recommend doing the maths in the real thing to be sure? Seems it might be worth the extra time.



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    (Original post by Adangu)
    I think again it is m/r^2

    *sorry for bad quality


    Thanks I did that but then expanded the brackets ((


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    Am I right with the working at the end to get it to equal 1/3


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    (Original post by gcsestuff)
    Thanks I did that but then expanded the brackets ((


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    Am I right with the working at the end to get it to equal 1/3


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    Yes thats right
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    (Original post by CD223)
    I see thank you everyone!

    What confused me is the maths and logic seemed to contradict each other! I'll try and redo the question another time and see if I get the correct answer.

    Would you recommend doing the maths in the real thing to be sure? Seems it might be worth the extra time.



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    It really depends on the question doesn't it? I think it's one of those ones where we just have to wait and find out!
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    (Original post by gcsestuff)
    What about question 13 on that paper. I can't seem to get it
    Question 13:
    There is no resultant field strength so:

    

\dfrac{GM}{y^2} = \dfrac{G \times 4M}{(d-y)^2}

    

\therefore \dfrac{1}{y^2} = \dfrac{4}{(d-y)^2}

    

\therefore \dfrac{y^2}{(d-y)^2} = \dfrac{1}{4}

    

\therefore \dfrac{y}{(d-y)} = \dfrac{1}{2}

    

\therefore 2y = d-y

    

\therefore 3y = d

    

\therefore \dfrac{y}{d} = \dfrac{1}{3}


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    (Original post by Adangu)
    It really depends on the question doesn't it? I think it's one of those ones where we just have to wait and find out!
    Good point. Hate these kinds of questions where tons of maths is just as effective as logical thinking :L


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    (Original post by CD223)
    I see thank you everyone!

    What confused me is the maths and logic seemed to contradict each other! I'll try and redo the question another time and see if I get the correct answer.

    Would you recommend doing the maths in the real thing to be sure? Seems it might be worth the extra time.



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    If you can see it with the logic, I would recommend doing it by logic first - this is probably what the exam writers intend, as it's only one mark. Put a squiggle or something next to that question on your paper, and if you've got time at the end come back and do the maths to double check
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    (Original post by Lau14)
    If you can see it with the logic, I would recommend doing it by logic first - this is probably what the exam writers intend, as it's only one mark. Put a squiggle or something next to that question on your paper, and if you've got time at the end come back and do the maths to double check
    Might have to do that! What time split are you aiming for with the written/MC?


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    (Original post by CD223)
    Might have to do that! What time split are you aiming for with the written/MC?


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    Less than 45 minutes total on the mc, but otherwise however long it takes! I go between the two halves anyway so it usually balances okay. How about you?
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    (Original post by Lau14)
    Less than 45 minutes total on the mc, but otherwise however long it takes! I go between the two halves anyway so it usually balances okay. How about you?
    Oh nice, I always tend to do one followed by the other

    Hoping for 40 minutes on the MC and 65 on the written as I take literally ages to write out answers.


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    https://m.youtube.com/watch?v=gQK21572oSU

    Nice 5 minute revision break about shm.


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    (Original post by gcsestuff)
    https://m.youtube.com/watch?v=gQK21572oSU

    Nice 5 minute revision break about shm.


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    If a 6 marker on bridges comes up then that revision break might come in handy


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    (Original post by CD223)
    Oh nice, I always tend to do one followed by the other

    Hoping for 40 minutes on the MC and 65 on the written as I take literally ages to write out answers.


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    Sounds good! Can't believe how fast proper exam season has come up :/
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    (Original post by CD223)
    If a 6 marker on bridges comes up then that revision break might come in handy


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    Could you imagine that! I'd be looking at the paper just grinning to myself


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    (Original post by Lau14)
    Sounds good! Can't believe how fast proper exam season has come up :/
    Me too! First exam of 7 on Friday

    (Original post by gcsestuff)
    Could you imagine that! I'd be looking at the paper just grinning to myself
    Lol! Me too. Gonna revise SHM and applications just in case


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    (Original post by CD223)
    Me too! First exam of 7 on Friday



    Lol! Me too. Gonna revise SHM and applications just in case


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    I have one on Wednesday and two on Friday this week :/ all my easier ones though at least so I can focus on physics for next week
 
 
 
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