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

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    6 marker:

    Talking about circular motion in the context of the mass on a string.
    V is changing but speed is constant - dirrection always changing therefore accelerates
    Force (centripetal) acts perpendicular to direction of motion - conditions for u.c.m
    Centriptal force provided by cent acc
    tension in string acts as centr - force

    difficult to demonstarte horizontally:
    theres mass which is acted on by gravity thus downward component makes it harder to veer perfectly horizontal,
    measuring this accuracy is a hard thing to do practically

    anything I may have missed?
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    (Original post by AR_95)
    YES MAN FINALLY A QUESTION I ACTUALLY GOT RIGHT LOOOOOOL

    i was stuck on this one for 20 minutes. Was kicking myself because I had done it before in a past paper!!!
    lol 20 minutes for 1 mark, what a bargain

    Just hoping the grade boundaries don't change significantly
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    (Original post by Mehrdad jafari)
    We literally had thousand hours of discussion about such a question


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    I came and got involved at the wrong time then ))))))
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    Well I felt okay about that paper until I realised the mistakes I'd made:

    • Didn't half the 4.4x10^10 electrons
    • Said there was no effect on damping
    • Said steel was to reduce power losses
    • Messed up the question on coils P and Q.

    Ffs.


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    (Original post by Amanzz)
    That's true, I was illustrating that stokes' law depends on velocity, which doesn't change what a new mass is added provided that there isn't a large change in surface area.


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    That analysis wouldn't necessarily apply because "radius" isn't well-defined for non-spherical objects, so the variables involved could be different altogether.
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    (Original post by NEWT0N)
    lol 20 minutes for 1 mark, what a bargain

    Just hoping the grade boundaries don't change significantly
    not sure why it was so long, every other question I did fine and I finished the MC in 35 minutes ( leaving the capacitor one for the end)
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    (Original post by CD223)
    Well I felt okay about that paper until I realised the mistakes I'd made:
    • Said there was no effect on damping

    I also said there was no effect on damping but how is that wrong? Surely the surface area is a key factor in determining damping.
    As surface area remains the same damping isn't affected by the ring.

    I could be wrong though.
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    (Original post by CD223)
    Well I felt okay about that paper until I realised the mistakes I'd made:

    • Didn't half the 4.4x10^10 electrons
    • Said there was no effect on damping
    • Said steel was to reduce power losses
    • Messed up the question on coils P and Q.

    Ffs.
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    Why do the electrons halve? Can't quite remember the question but I know I didn't!
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    i think it was easier to lose marks this year than last years, very awkward wordy questions and a lot of tricks. I think grade boundaries may drop slightly ie a mark or 2
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    (Original post by CD223)
    Well I felt okay about that paper until I realised the mistakes I'd made:

    Didn't half the 4.4x10^10 electrons
    • Said there was no effect on damping
    Said steel was to reduce power losses
    • Messed up the question on coils P and Q.

    Ffs.


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    I did those as well (the ones in bold)

    Chin up, I'm sure you'll be fine. If that's really the total number of mistakes you made you're still looking at a high (full UMS even?) A*. I'm hoping for either just scraping full UMS but hopefully an A* in any case, although the fact that there are like 5 marks between each grade is slightly worrying
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    (Original post by CD223)
    Well I felt okay about that paper until I realised the mistakes I'd made:

    • Didn't half the 4.4x10^10 electrons
    • Said there was no effect on damping
    • Said steel was to reduce power losses
    • Messed up the question on coils P and Q.

    Ffs.


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    It's all cool man. I'm sure i made more mistakes than you did but I'm very happy with the exam. For me making mistakes is not a problem, but not learning anything from them is a problem.


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    (Original post by QueNNch)
    I also said there was no effect on damping but how is that wrong? Surely the surface area is a key factor in determining damping.
    As surface area remains the same damping isn't affected by the ring.

    I could be wrong though.
    It also relies on momentum
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    (Original post by Lau14)
    I haven't heard anyone else notice this yet, but it would be bad if they had messed up!
    It was mentioned a lot earlier up the thread!
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    (Original post by Lau14)
    Why do the electrons halve? Can't quite remember the question but I know I didn't!
    The question asked for the number of electrons on the NEGATIVE plate ONLY.

    As each capacitor plate shares equal number of electrons it is halved.
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    (Original post by Chazley123)
    6 marker:

    Talking about circular motion in the context of the mass on a string.
    V is changing but speed is constant - dirrection always changing therefore accelerates
    Force (centripetal) acts perpendicular to direction of motion - conditions for u.c.m
    Centriptal force provided by cent acc
    tension in string acts as centr - force

    difficult to demonstarte horizontally:
    theres mass which is acted on by gravity thus downward component makes it harder to veer perfectly horizontal,
    measuring this accuracy is a hard thing to do practically

    anything I may have missed?
    I reckon you will get 4/6. I wrote similar but my teacher said you had to state that the tension in the string resolved vertically TSin(x) would be equal to mg if it is to remain horizontal. Also explain the 3 laws in context
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    (Original post by QueNNch)
    Your argument is valid but I've also done Q 20 in past papers and it's definitely -322

    Change in direction of current, making force apply in opposite direction. (Flemings LHR)
    I know i've just looked, it's where the initial reading was zeroed, therefor it can have a negative value as mass already acts on the scales
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    (Original post by Chazley123)
    6 marker:

    Talking about circular motion in the context of the mass on a string.
    V is changing but speed is constant - dirrection always changing therefore accelerates
    Force (centripetal) acts perpendicular to direction of motion - conditions for u.c.m
    Centriptal force provided by cent acc
    tension in string acts as centr - force

    difficult to demonstarte horizontally:
    theres mass which is acted on by gravity thus downward component makes it harder to veer perfectly horizontal,
    measuring this accuracy is a hard thing to do practically

    anything I may have missed?
    You do realize it is impossible to do it perfectly horizontally... not harder.

    BECAUSE: there is no vertical component of the tension to counter act the weight of the ball.
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    (Original post by Sonnyjimisgod)
    I reckon you will get 4/6. I wrote similar but my teacher said you had to state that the tension in the string resolved vertically TSin(x) would be equal to mg if it is to remain horizontal. Also explain the 3 laws in context
    examiners forever wanting you to go further :/
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    (Original post by AR_95)
    not sure why it was so long, every other question I did fine and I finished the MC in 35 minutes ( leaving the capacitor one for the end)
    Nice, I think I did exactly 45 minutes on MC or slightly lower but I remember making some mistakes while filling the answer sheet which cost me a few minutes to fully check through and re-check (the last thing you want is to fill out the answer sheet wrong!)
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    (Original post by chizz1889)
    It also relies on momentum
    The alternative answer which would oppose my thoughts is that if it has a greater mass it has more mgh and then it has a greater 1/2mv² and so there is a greater drag force. I thought the damping force was only because of drag on a pendulum, so I really don't know which solution is correct.


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