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

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    Rate of change of momentum is Ns/s = N?
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    (Original post by Disney0702)
    How is the first question acceleration.
    Is rate of change of momentum really acceleration?
    Yeah, thats how F=ma is derived


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    (Original post by Humbers)
    It was rotated horizontally so weight is perpendicular to centripetal force therefore ignored

    T = mv^2/r 0.25 x 8.6^2 / 1.5 = 12.3N
    I put T = +F
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    (Original post by DannySmith420)
    I think thats wrong because the weight of particle is not taken into account. I did T - mg = mv^2/r
    It said assume string is horizontal though


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    (Original post by Mehrdad jafari)
    Here are my answers. The ones I'm not sure with i have mentioned next to them.

    I have failed to take the answer of one of the MC questions. Let me know if you found which one.
    I would be very happy if you could correct the ones that are not right
    Attachment 425411
    Thanks for putting them!

    I think you question 17 is incorrect because the question asked for the number on electrons on the NEGATIVE plate ONLY. Therefore the answer is half of what you got. (something like 2.2 x 10^10)

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    (Original post by fruity97)
    I got 15N at first for tension! But I remember changing it towards the end to 12N because I didn't include the weight I think? Stil not sure which is right but they said horizontal so I changed it
    Yeah that's why I think it's wrong :/
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    (Original post by wat a wizard)
    Rate of change of momentum is Ns/s = N?
    Yes. Rate of change of momentum is directly proportional to force (this is the momentum version of Newton II). Therefore the answer was D, weight.
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    (Original post by Mehrdad jafari)
    Here are my answers. The ones I'm not sure with i have mentioned next to them.

    I have failed to take the answer of one of the MC questions. Let me know if you found which one.
    I would be very happy if you could correct the ones that are not right
    Attachment 425411


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    Pretty sure 22 was 1/rt2 maybe you forgot to root each side?
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    (Original post by Mehrdad jafari)
    Here are my answers. The ones I'm not sure with i have mentioned next to them.

    I have failed to take the answer of one of the MC questions. Let me know if you found which one.
    I would be very happy if you could correct the ones that are not right
    Attachment 425411


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    First one is weight
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    Omg. I did not have enough time!! :'(
    Guessed like some of the MC question. Fml.

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    (Original post by Fred Cantoni)
    No. It's force.


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    Yh thats what I thought as well. Did u put weight as your answer?
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    (Original post by Sbarron)
    Re-read what i put. I didn't say that t was affected by m.... I meant that t wasn't affected and therefore no damping because for damping to occur t would be affected
    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.
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    (Original post by NEWT0N)
    This is an unfair advantage for you then, because if they decide to mark it as "150 ohms" then people who got confused by the "150 k ohms" will maybe have drawn a different current intercept due to the confusion. So they would have to mark it like this I think:

    Any current less than the original current should get the first mark

    Shallower gradient gets the second mark

    Anyone agree?
    Sounds fair!
    What about the 3rd mark?


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    (Original post by QueNNch)
    Thanks for putting them!

    I think you question 17 is incorrect because the question asked for the number on electrons on the NEGATIVE plate ONLY. Therefore the answer is half of what you got. (something like 2.2 x 10^30)

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    Damn, yeah, if they asked for one of the plates only then its half


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    (Original post by Fvthoms)
    55 for A*
    50 for A
    etc...
    What is it out of again?
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    (Original post by fruity97)
    Yeah what we're aqa playing at! Did they mean 150kohms? My graph was so small
    Surely if they were charged with the same voltage the initial current should be the same. They were juat discharged through different resistors. So I drew a shallower graph?😕
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    (Original post by Fred Cantoni)
    Sounds fair!
    What about the 3rd mark?


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    There were 3? Hm, maybe they would want you to extend the graph to cover the whole length of the x-axis or something. Or they would not want it to intercept the x-axis but only tend asymptotically to it. I don't know
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    (Original post by Mehrdad jafari)
    Yeah, thats how F=ma is derived


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    So shouldn't it be a force unit not acceleration?
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    (Original post by NEWT0N)
    What is it out of again?
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    (Original post by Fred Cantoni)
    It said assume string is horizontal though



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    Ah right yeah i see, **** !
 
 
 
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