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

OP

Original post by EmiratesCaptain

Should have said 'by astronomical units!' :wink:

That pun... Was out of this world.

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Reply 2161

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/AQA-PHYA4-2-QP-JUN12.PDF

MS:http://filestore.aqa.org.uk/subjects/AQA-PHYA4-W-MS-JUN12.PDF

Reply 2162

Jimmy20002012

4

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/AQA-PHYA4-2-QP-JUN12.PDF

MS:http://filestore.aqa.org.uk/subjects/AQA-PHYA4-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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Reply 2163

_Caz_

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/AQA-PHYA4-2-QP-JUN12.PDF

MS:http://filestore.aqa.org.uk/subjects/AQA-PHYA4-W-MS-JUN12.PDF

That's part iii) hope it helps :smile:

1432925748953.jpg55.4KB

Reply 2164

_Caz_

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/AQA-PHYA4-2-QP-JUN12.PDF

MS:http://filestore.aqa.org.uk/subjects/AQA-PHYA4-W-MS-JUN12.PDF

I had a go of explaining part c too :smile:

hope this helps a little bit if you can read my rubbish writing

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1432926143869.jpg68.9KB

Reply 2165

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?

Reply 2166

_Caz_

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

Reply 2167

Original post by _Caz_

Yep

Thanks man that was very helpful :smile:

Reply 2168

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.

Reply 2169

Disney0702

9

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.

Reply 2170

sam_97

6

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". :smile:

Reply 2171

OP

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". :smile:

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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Reply 2172

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/AQA-PHYA4-1-QP-JAN13.PDF

Reply 2173

OP

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/AQA-PHYA4-1-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:
ImageUploadedByStudent Room1432984801.628136.jpg

ImageUploadedByStudent Room1432984801.628136.jpg

Reply 2174

OP

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/AQA-PHYA4-1-QP-JAN13.PDF

And question 12:
ImageUploadedByStudent Room1432984825.479479.jpg

Sorry I don't have the others! Let me know if you still need help when I'm back at home :smile:

Reply 2175

ImageUploadedByStudent Room1432986814.002696.jpg

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 :smile:

)

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Reply 2176

ImageUploadedByStudent Room1432987088.510587.jpg

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 :smile:

Reply 2177

Sorry this is the other question ImageUploadedByStudent Room1432987214.375637.jpg

Reply 2178