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# AQA Physics PHYA4 - 20th June 2016 [Exam Discussion Thread] watch

1. (Original post by Euclidean)
Nope. Because V is a magnitude.

0 = mv - NV

So:

NV = mv

V = mv/N

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old momentum = 0
new momentum = 0
VN+mv=0
because the value of v and V already account for the different directions.
but the mark scheme will probably not care
V is not a magnitude, it said Velocity V
2. (Original post by johnapplebottom)
no wat, 220 was the nuclean number before it decayed by alpha particle thing
so after it was 220-4 = 216
Yup
3. (Original post by duncant)
what did people say about the B- emission any why the equations wouldnt work? I said that B emission is an electron which isnt a nucleon, which is what the equations represent?
Mass isn't conserved - neutron turns into proton emitting B-
4. (Original post by IMZL)
120 UMS boundary predictions?
I recon 66?
5. (Original post by IMZL)
120 UMS boundary predictions?
62/75 - higher than last year, but multiple choice was hard and there were a lot of wordy questions.
6. I got about 45? Will i get at least 80 Ums marks?
7. do you get a mark for saying electricity can be generated from the brakes to power the car to reduce fuel consumption and for disadvantage that in emergency situations the brakes may not slow down quick enough
8. Annoyingly, was going to say the x-axis was the time period squared to give a straight gradient based on the equation but bottled it. Also, I said Emf induced is *proportional* to the rate of change magnetic flux as opposed to *directly proportional*, are we thinking I'll lose the marks on that one?
9. (Original post by thestudntrm)
Mass isn't conserved - neutron turns into proton emitting B-
How is it not conserved? The proton is less massive than the neutron. Don't forget an antineutrino is produced which takes momentum (and hence energy) from the decay away, so the equations won't work; it's a three body process.
10. (Original post by particlestudent)
How many marks was the derivation for Venus and then working it's R out
I think it was 4 for the proof then 2 for calculating R.
11. (Original post by Blackmagic123)
old momentum = 0
new momentum = 0
VN+mv=0
because the value of v and V already account for the different directions.
but the mark scheme will probably not care
V is not a magnitude, it said Velocity V
It did say velocity I agree, BUT the arrows were in opposite directions!
12. (Original post by EdwinLangley)
I did the exact same thing unfortunately - noticed my mistake coming out.

You get that time constant if you took Q/Q0 to be 0.8 rather than 0.2...

Sorry - hope we didn't lose many marks for it and get ECF for the resistance
I did the same but then got a stupidly large time constant of like 88000 so knew it was wrong.
13. (Original post by IMZL)
It's in the opposite direction so mv-NV=0 but that means V=mv/N not -mv/N.
Yes and I got the derivation correct using the positive version so it must be correct
14. (Original post by Jordenwilder1998)
do you get a mark for saying electricity can be generated from the brakes to power the car to reduce fuel consumption and for disadvantage that in emergency situations the brakes may not slow down quick enough
I put the same for the advantage. Pretty sure that electromagnetic braking is faster than regular braking . . .
15. Say 66 was 120 UMS boundary, would there be any advantage in getting over 66 in terms of how well you'd need to do in unit 5?
16. (Original post by ombtom)
Back to the V = ±mv/N thing...

V and v are velocities.

The velocities are in different directions, as shown by the arrows in the diagram.

Since they are in different directions, V must equal -mv/N.

SOMEONE HELP.
momentum before is 0

mv-MV=0
mv=MV
V=mv/M
17. (Original post by wallpaperpaste)
Yes and I got the derivation correct using the positive version so it must be correct
Positive version is correct but you would still get correct derivation with negative.
18. (Original post by wallpaperpaste)
Yes and I got the derivation correct using the positive version so it must be correct
Likewise
19. (Original post by IMZL)
Say 66 was 120 UMS boundary, would there be any advantage in getting over 66 in terms of how well you'd need to do in unit 5?
No, once you reach the 120 UMS boundary then you can get no more UMS from that paper.
20. Does anyone remember what the densit of the planet was, for which we had to find R?

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