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# EDEXCEL A2 Physics EXAM Unit 4 Physics On The Move 20th June 2016 (NOT I-A-L)

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1. I couldn't see a thread for this so I started one.

I have put together some videos and Unit 4 Paper Walkthroughs
on my youtube channel

Good luck with your exams everybody!

EJS
2. (Original post by ElvishJumpSuit)
I couldn't see a thread for this so I started one.
I put this thread in the A Level Exam Directory Mega Thread for you which you can find here use that thread to find discussions about your other exams too
3. Hey, thanks for making this thread, was hoping there'd be one to talk about this exam (and maybe the unit five one too). Hopefully it'll liven up around here
4. I was feeling confident, until i did the jan12 paper
5. Could anyone explain these two questions to me please? I'm really confused.
6. (Original post by target21859)
Could anyone explain these two questions to me please? I'm really confused.
15) it's a ratio, so when you measure the actual thickness of the lead plate using a ruler it says its 4mm thick (so a 2:3 ratio) so measure the radius (along the lead plate) and then multiply by the ratio

5) F=BILsintheta

however, you ignore the angle because you are looking at the QS side which is perpendicular to the field. so its just BIL multiplied by the number of turns.
7. (Original post by Lh22)
15) it's a ratio, so when you measure the actual thickness of the lead plate using a ruler it says its 4mm thick (so a 2:3 ratio) so measure the radius (along the lead plate) and then multiply by the ratio

5) F=BILsintheta

however, you ignore the angle because you are looking at the QS side which is perpendicular to the field. so its just BIL multiplied by the number of turns.
But the question says the plate is 6mm thick. Also for 5 if there the wire is a coil with N turns then is the general formula F=NBilsinx?
edit: I understand why now for 15. It's a different scale makes sense but I don't understand how you measure the radius. Would just use a compass and find a centre point which follows the curve and measure that?
8. (Original post by target21859)
But the question says the plate is 6mm thick. Also for 5 if there the wire is a coil with N turns then is the general formula F=NBilsinx?
edit: I understand why now for 15. It's a different scale makes sense but I don't understand how you measure the radius. Would just use a compass and find a centre point which follows the curve and measure that?
yeah, you would estimate a radius by taking couple using a protractor. The range of answers is pretty wide for that reason.
9. Could someone explain to me how one would go through this momentum question?:

"A spacecraft initially at rest of mas 20000 kg fires its rocket which expels 100 kg of gas every second at a speed of 100 m/s. How long would the rocket have to be fired for to accelerate the rocket to a speed of 50 m/s?"
10. (Original post by JammyW15)
Could someone explain to me how one would go through this momentum question?:

"A spacecraft initially at rest of mas 20000 kg fires its rocket which expels 100 kg of gas every second at a speed of 100 m/s. How long would the rocket have to be fired for to accelerate the rocket to a speed of 50 m/s?"

This is a bit of a tricky question in that the acceleration isn't constant but knowing that the rate of change of acceleration is constant (see acceleration time graph) allows you to find the answer which is 100 seconds to reach 50m/s. Let me know if this makes any sense!
11. (Original post by CasioGamer98)

This is a bit of a tricky question in that the acceleration isn't constant but knowing that the rate of change of acceleration is constant (see acceleration time graph) allows you to find the answer which is 100 seconds to reach 50m/s. Let me know if this makes any sense!

Ahhhh yeah, I understand it now. Thank you very much for that
12. Props to OP, those are some great videos.
13. Can somebody please help explain to whether this is correct as a answer for the question

https://gyazo.com/6b45c663dd5984fc8b40413733d335a0

I said

- When a capacitor builds up charge, the movement of electrons travel across the 2 plates.
(that capacitor = sign on a circuit).
- It fully charged when pd of capacitor is equal to the pd of the supply.

I don't understand this on the mark scheme ---> "when fully charged there is no movement of electrons"
Is that because C = Q/V .*. when C = max .*. V has to be a small value .*. emf is a small value/rate of flow of charged particles is smaller.
14. (Original post by XxKingSniprxX)
Can somebody please help explain to whether this is correct as a answer for the question

https://gyazo.com/6b45c663dd5984fc8b40413733d335a0

I said

- When a capacitor builds up charge, the movement of electrons travel across the 2 plates.
(that capacitor = sign on a circuit).
- It fully charged when pd of capacitor is equal to the pd of the supply.

I don't understand this on the mark scheme ---> "when fully charged there is no movement of electrons"
Is that because C = Q/V .*. when C = max .*. V has to be a small value .*. emf is a small value/rate of flow of charged particles is smaller.
The question is getting at the fact electrostatic repulsion of electrons off the positive plate becomes exponentially harder as charge builds up. So initially there's a large flow of charge (high current) but as it becomes fully charged no charge flows so no electrons are moving.

Also remember the capacitance of a non variable capacitor like the one shown doesn't change so its always at the same value.
15. Should all numerical answers be given to 3 sgf or does it depend on the data provided ?? If so, please elaborate. Thanks !!
16. (Original post by omar5478)
Should all numerical answers be given to 3 sgf or does it depend on the data provided ?? If so, please elaborate. Thanks !!
Depends on data provided, give the same amount of significant figures as it, or maximum of one more.

E.g if you see 2.5x10^-6 Farads give any answer to two or three SF.

17. Hey, can someone explain how to do this question to me please?
18. (Original post by _leenz)

Hey, can someone explain how to do this question to me please?
Ek = eV
Ek = 1/2mv^2

eV = 1/2mv^2

V = mv^2/2e

.*. Answer is A.
19. (Original post by omar5478)
Should all numerical answers be given to 3 sgf or does it depend on the data provided ?? If so, please elaborate. Thanks !!
Also, I could be wrong, but I think with show that questions you need to give more significant figures than they have.
E.g show that ___________ is approximately 1 x 10^8
You would give the answer 1.32 x 10^8

Posted from TSR Mobile
20. Anyone been memorizing mark schemes for the written questions? Which ones?

So far I've only done the Rutherford Geiger Marsden ones and the cyclotron/linac/detector questions

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