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    (Original post by tishysquishy)
    it was a bit pants i thought
    I had a blank and totally forgot Hookes law HOOKES LAW! the godamn easiest little thing to remember! grrrrr....
    What ya'll think the A grade percentage will b? 70%?
    i forgot hookes law as well lol, coudlnt prov that l-lo thing i just wrote out the 2πf=l/g and l must =l-lo as this is the length being tested. or some rubbish. was only a couple of marks though.
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    sorry thats a mean thing to say!
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    for the question about hooke's law you had the equation for time period of mass on spring. you just squared it and substituted k=F/e => mg/l-lo into the original equation squared

    i did the de broglie wavelength question, after the question about working out speed of electron. but i dont remember anything to do with ratios?
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    (Original post by mr_shoe_uk)
    Yeah, that question about the sonar was quite nice.

    The very opening question was one of those with loads of steps though. First you needed to use the potential energy formula, then know what power is work done divided by time taken, then work out the electrical power supplied, then do the efficiency as power out/power in! They could have made a whole question out of that, instead it was a tiny part! ..I think it was 11.1%?
    Ye 11% here too
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    (Original post by deity47)
    Ye 11% here too
    mee too! yayayayyaay 3 marks!
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    (Original post by tishysquishy)
    mee too! yayayayyaay 3 marks!
    so we are all agreed on 11% then , w00tz
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    mr_shoe_uk you just had to use the power value they gave you. use P = FV and divide them
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    reckon A boundary will be around 75% - normally is around that.. wasn't anything insanely hard in this paper to push it any lower.

    MdSalih
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    does anyone know marks per question etc? and with an ickle description of what they are etc? just so i can try and assume what i got and weep
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    (Original post by deity47)
    Distance = speed x time I'm sure you meant :p:

    :rolleyes: ahhh sod it, i checked my units in the exam and they were fine. but yeth, that equation lol

    I got 11% 2sf for the efficiency
    GCSE stuff again on that one:
    E = P x t = I x V x t
    The only question I can think I blagged was V=-g/R. Was it meant to be as simple as stating V=-GM/r and g=-GM/r2 ?
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    was the ratio question the de broglie question After the question about electron speed ?
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    (Original post by corkskrew)
    :rolleyes: ahhh sod it, i checked my units in the exam and they were fine. but yeth, that equation lol

    I got 11% 2sf for the efficiency
    GCSE stuff again on that one:
    E = P x t = I x V x t
    The only question I can think I blagged was V=-g/R. Was it meant to be as simple as stating V=-GM/r and g=-GM/r2 ?
    yaa and then saying that E = V x 1/r
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    (Original post by tishysquishy)
    yaa and then saying that E = V x 1/r
    Score. Hmm having not done maths since gcse I'm actually quite happy. Only 51 days til results day now...
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    (Original post by xelprep)
    was the ratio question the de broglie question After the question about electron speed ?
    Think so!
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    lol, i got a ratio of 1E7:1................ i think that MAY be wrong.... whoopsie
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    (Original post by xelprep)
    was the ratio question the de broglie question After the question about electron speed ?

    Yeah ratio of speed of electron to circumferrence of orbit or some such jazz
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    I think I did alright on that paper but there were some areas where it was quite hard.

    Didn't anyone else think that for the first question you had to do a ridiculous amount of work for 3 marks?!

    The last question was really bad ... I got onto that question with about 15 minutes to go and my mind went blank. I wasn't able to work out the electron speed (although I now know you were supposed to use F = mv²/R ...) and so I wrote down any random wrong answer. Therefore I proceeded to do the last part of that question (working out that ratio), using my incorrect value for the speed.

    Do you think I'll get consequential marks?

    Another thing which I think I messed up was when I was asked to find "l0" from that graph. I didn't draw my graph wide enough to find out the x-intercept. So therefore I used the value of "g" and some of the values from the table to find out "l0" by algebra. I got 300mm which matched what other people said, but I used the wrong method. Do you think they'll mind?

    And one last thing which I thought was tricky was proving that formula:

    Gravitational Field Strength = - Gravitational Potential / Radius

    How did you go about proving there was a minus sign in the final answer?
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    (Original post by mr_shoe_uk)
    It was ok.

    Some questions, especially on the last page, seemed like you had to do loads of steps within each little question. Did anyone get the speed of the electron to be something * 10-4 ms-1? First I wasn't sure how it could be so slow, but then realised that it's travelling round such an incredibly miniscule distance.

    I messed up the graph somehow. I got g to be 10.2, which isn't too far off, so I can't have been all wrong, but I got some stupid negative answer for the original length.

    Also, wasn't sure how we were meant to show that some oxygen would escape the moon. I worked out the average kinetic energy would be less than the potential energy.

    I'll take them in order:

    i) So long as you got the ratio in (c) to be 1, then you'll probably be right. Most people seem to have got 1, including myself.

    ii) I got l0 = 63.5mm. Drew a graph, and got a negative intercept (about -24mm). Splitting the equation into the form y = mx + c gave the equation of the y-intercept to be - 4(pi)2l0/g. Using g = 10000.1 ish mm s-2 will get you a positive value for l0 as the minus signs cancel.

    iii) I said that the value calculated was only the average KE. So some and not all (which was in the question) would escape because some would have KE bigger than the GPE calculated whereas most will not.
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    (Original post by junners)
    How did you go about proving there was a minus sign in the final answer?
    By simply writing in the last line of my derivation without giving a reason, as far as I remember. They in the opposite direction?
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    (Original post by junners)
    Another thing which I think I messed up was when I was asked to find "l0" from that graph. I didn't draw my graph wide enough to find out the x-intercept. So therefore I used the value of "g" and some of the values from the table to find out "l0" by algebra. I got 300mm which matched what other people said, but I used the wrong method. Do you think they'll mind?
    lol hope not cos thats what i did too! i make the graph nice and big... then realising i need an intercept sumwhere
 
 
 
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