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

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    (Original post by EmiratesCaptain)
    Should have said 'by astronomical units!'
    That pun... Was out of this world.


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    Does anybody know where the 0.17 comes from for question 1biii and why there are bumps on the graph for part c? Thanks a lot.

    QP: http://filestore.aqa.org.uk/subjects...2-QP-JUN12.PDF

    MS:http://filestore.aqa.org.uk/subjects...W-MS-JUN12.PDF
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    (Original post by JJBinn)
    Does anybody know where the 0.17 comes from for question 1biii and why there are bumps on the graph for part c? Thanks a lot.

    QP: http://filestore.aqa.org.uk/subjects...2-QP-JUN12.PDF

    MS:http://filestore.aqa.org.uk/subjects...W-MS-JUN12.PDF
    Force is equal to the rate of change of momentum.

    F=delta mv/delta t
    mg=1.68
    m= 1.68 x 9.81


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    (Original post by JJBinn)
    Does anybody know where the 0.17 comes from for question 1biii and why there are bumps on the graph for part c? Thanks a lot.

    QP: http://filestore.aqa.org.uk/subjects...2-QP-JUN12.PDF

    MS:http://filestore.aqa.org.uk/subjects...W-MS-JUN12.PDF
    That's part iii) hope it helps

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    (Original post by JJBinn)
    Does anybody know where the 0.17 comes from for question 1biii and why there are bumps on the graph for part c? Thanks a lot.

    QP: http://filestore.aqa.org.uk/subjects...2-QP-JUN12.PDF

    MS:http://filestore.aqa.org.uk/subjects...W-MS-JUN12.PDF
    I had a go of explaining part c too hope this helps a little bit if you can read my rubbish writing

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    Thanks for the efforts guys, really appreciate it. I understand it now I think, just one last thing, the 1.68N is the force at a given second. So is that basically saying you have an extra mass of 0.17kg at a given second due to the extra weight from momentum and this is why it is irrespective of the fact it's 10 seconds in total?

    So if the question asked about the mass after 20 seconds, the amount you add for the momentum would always be 0.17?
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    (Original post by JJBinn)
    Thanks for the efforts guys, really appreciate it. I understand it now I think, just one last thing, the 1.68N is the force at a given second. So is that basically saying you have an extra mass of 0.17kg at a given second due to the extra weight from momentum and this is why it is irrespective of the fact it's 10 seconds in total?

    So if the question asked about the mass after 20 seconds, the amount you add for the momentum would always be 0.17?
    Yep

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    Thanks man that was very helpful
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    Is the mark scheme strict with the numerical values for answers in this paper? As in if you're doing the right thing, but your answer is very slightly different from the one they've put.
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    (Original post by FN510)
    Is the mark scheme strict with the numerical values for answers in this paper? As in if you're doing the right thing, but your answer is very slightly different from the one they've put.
    Yes they are!

    You have to make sure you put any numerical answer in the correct number of significant figures.

    Unfortunately they do not usually tell you what is the correct number of significant figures is, it is something that you'll have to figure out when you tackle the questions.

    It is usually 2 or 3 significant figures.

    People usually do not score the final answer mark just because they didn't round it to the correct significant figure even if their answer is correct.
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    (Original post by Disney0702)
    Yes they are!

    You have to make sure you put any numerical answer in the correct number of significant figures.

    Unfortunately they do not usually tell you what is the correct number of significant figures is, it is something that you'll have to figure out when you tackle the questions.

    It is usually 2 or 3 significant figures.

    People usually do not score the final answer mark just because they didn't round it to the correct significant figure even if their answer is correct.
    Incorrect significant figures only get penalised in certain questions. There are usually 1 or 2 of these questions in each paper and they always say "Give your answer to an appropriate number of significant figures".
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    (Original post by sam_97)
    Incorrect significant figures only get penalised in certain questions. There are usually 1 or 2 of these questions in each paper and they always say "Give your answer to an appropriate number of significant figures".
    That's true. I find it funny when I give so many incorrect number of sig figs on the questions that don't worry about it and then suddenly give the correct number on the question that asked for it :L


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    Not understanding how to get the efficiency on 25, whenever I do it it comes out as about 68%, really weird. I am also confused over 10,12 and 13 although I managed to get them right by judgement, I don't really understand them. If anybody could explain some/all of these questions that'd be awesome. Thanks

    http://filestore.aqa.org.uk/subjects...1-QP-JAN13.PDF
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    (Original post by JJBinn)
    Not understanding how to get the efficiency on 25, whenever I do it it comes out as about 68%, really weird. I am also confused over 10,12 and 13 although I managed to get them right by judgement, I don't really understand them. If anybody could explain some/all of these questions that'd be awesome. Thanks

    http://filestore.aqa.org.uk/subjects...1-QP-JAN13.PDF
    I'm out of the house at the moment but here's some workings I have on my phone saved from previous questions:

    Question 10:
    Name:  ImageUploadedByStudent Room1432984801.628136.jpg
Views: 65
Size:  70.7 KB


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    (Original post by JJBinn)
    Not understanding how to get the efficiency on 25, whenever I do it it comes out as about 68%, really weird. I am also confused over 10,12 and 13 although I managed to get them right by judgement, I don't really understand them. If anybody could explain some/all of these questions that'd be awesome. Thanks

    http://filestore.aqa.org.uk/subjects...1-QP-JAN13.PDF
    And question 12:
    Name:  ImageUploadedByStudent Room1432984825.479479.jpg
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    Sorry I don't have the others! Let me know if you still need help when I'm back at home


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    Name:  ImageUploadedByStudent Room1432986814.002696.jpg
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    Can anyone help me with 13, I know it acts downwards and I know field strength is constant but how do I work out the potential; thanks )


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    Name:  ImageUploadedByStudent Room1432987088.510587.jpg
Views: 157
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    Name:  ImageUploadedByStudent Room1432987088.510587.jpg
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    Can I have some help with these 2, I don't know what the formula/units for potential gradient are.

    And also for question 1 I've always just accepted this, how do you work it out


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    Sorry this is the other question Name:  ImageUploadedByStudent Room1432987214.375637.jpg
Views: 99
Size:  43.2 KB


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    Finally. Name:  ImageUploadedByStudent Room1432987716.262116.jpg
Views: 109
Size:  45.2 KBName:  ImageUploadedByStudent Room1432987726.909437.jpg
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Size:  44.3 KBName:  ImageUploadedByStudent Room1432987737.959531.jpg
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    I thought that the centripetal force acted towards the centre of oscillation? But the mark schemes answer says t=mv^2/l+mg

    Thanks for any help!


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    On average around 7 or 8 of the qyestions on the paper have been re used. Good to know 😉


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