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# AQA Physics PHYA5 - 28th June 2016 [Exam Discussion Thread] watch

1. (Original post by micycle)
Could someone explain how during fission, energy is released even though new nuclei have higher binding energy per nucleon.
E= mc^2. When fission occurs there's a mass defect. So using E= mc^2 you can find the energy released as E and mass are equivalent.
2. (Original post by Ainsleyy)
An astronomical unit is the distance between the earth and the sun. The table tells you the max distance between the sun and vesta. So the furthest vesta can be from the earth is the furthest it can be from the sun + the distance between the earth and the sun which is 1 AU.

2.57 + 1
Ohhhh okay thank you
3. (Original post by Ainsleyy)
Astrophysics question:

Can anyone help me with this question? Its the astro part of June2010 question 2bii. The question is in the spoiler. Thanks
Spoiler:
Show

Bump
4. (Original post by micycle)
Could someone explain how during fission, energy is released even though new nuclei have higher binding energy per nucleon.
Basically the energy released is the total change in binding energy. When fission occurs the daughter nuclei fall into a potential well, where they are then in a more stable state that the parent nuclei. In falling into the potential well energy is release as heat and now to bring them out of the potential well you have to supply energy to seperate the constituent protons and neutrons into the their free counterparts. The energy is sourced from the mass deficit as E=mc^2 and so the energy you supply goes into providing the mass that was lost in formation of the nuclei.
5. TURNING POINTS

Okay just finished relativity...still need to go through m&m experiemnt but I can cram that as it's just memorising

Just want to check my understanding

For time dilation, t0 is the time according to the clock on the fast moving object....and t is the time of the observers clock

Because with the twin paradox, the 1/(1-(v/c)^2)^0.5 is always <1 as v<c.

That means t0 is divided by less than 1 so increases....and the fast moving twin experiences less time so his clock must be t0?

For length contraction l0 is the length as measured by the observer on the fast moving object

And m0 is the mass according to slow observer?

God this is a touch confusing
6. were there no unit 5 January resits or have AQA just deleted them?
7. (Original post by Dann_a)
were there no unit 5 January resits or have AQA just deleted them?
There haven't been any January papers for a few years now. Same with all other subjects I think.
8. (Original post by lucabrasi98)
None of that makes any sense to me though. I'm not even sure what you mean by shortest time interval and largest. And i would've thought t0 was the biggest time.

But instead of worrying about it, i realised it doesn't need to make sense for me to ace the paper. It's fine as long as I can apply it, which I can. I just practiced time dilation questions until i wasn't dropping any marks.

I would ask my teacher to explain the theory but she says she doesn't get it. She claims it's because she only did a chemistry degree lol

The only thing I'm worried about now is that gas equation proof
Time interval meaning the time difference between any given two events.
9. (Original post by rory58824)
There haven't been any January papers for a few years now. Same with all other subjects I think.
Thats not the question I asked.......
I know they stopped doing them after 2013
10. How deep does our understanding of relativity need to be for turning points?

I recall it being to do with the fact that the front door events happened faster to the person on the ladder compared to the back door as the back door is behind and as its travelling at c it takes time to sort of catch up....also that what we oberve is what actually exists according to us 'the observer' as everything that impacts you from an image (force applied due to gravity or electrostatic force etc) travels at or slower than c....so if we see a distant star as still bright even though its long died it still actually exists to us as we feel the gravity/etc?

I havent done many past papers so windering how in depth we need to understand it?
11. (Original post by marcusman97)
M=50 and M= fo/fe, 50=fo/fe rearrange to fo = 50fe

Total length of telescope= fo + fe
fo + fe = 3.7

sub in fo=50fe

50fe + fe= 3.7 therefore 51fe=3.7
Thankyou!!
12. (Original post by Haleema567)
You make two equations:

Fo + Fe = 3.7
so Fo = 3.7 - Fe

Then substitute that into the second equation which is:

Fo/Fe = 50 so Fo = 50Fe
3.7 - Fe = 50Fe

and so 51Fe = 3.7

That's how they got 51
Thankyou!!
13. Where does the 3 at the bottom come from in the rms formula?

Pressure through x plane= (Nmu^2)/V, and then when derived in terms of y and z components, it's the same but with v and w instead of u.

Surely when you add all of these together you get p= (3Nm)/V * (u^2 + v^2 + w^2) but the book says its Nm/3V, why?

Protoxylic
14. Can someone quickly explain something to me? I understand that, during fusion, energy is released because when the two smaller nuclei fuse together, the mass of the new nucleus is less than the mass of the two nuclei that were fused. This causes a mass difference, which releases energy (due to E= mc^2). What is the case with fission? Is it that the mass of the smaller nuclei released is less than the nucleus, causing the same situation as in fusion? or is it that the mass of the smaller nuclei released is greater? I'm slightly confused here. (I do understand that energy is released when binding energy per nucleon is released, but I am wondering about what happens with the mass)
15. (Original post by particlestudent)
Where does the 3 at the bottom come from in the rms formula?

Pressure through x plane= (Nmu^2)/V, and then when derived in terms of y and z components, it's the same but with v and w instead of u.

Surely when you add all of these together you get p= (3Nm)/V * (u^2 + v^2 + w^2) but the book says its Nm/3V, why?

Protoxylic
It is derived in terms of looking in one dimension therefore you divide by 3 because on average a 1/3 of the gas molecules will have non-zero velocity in the x-direction. You then replace the speed by the root mean square speed.
16. (Original post by Protoxylic)
It is derived in terms of looking in one dimension therefore you divide by 3 because on average a 1/3 of the gas molecules will have non-zero velocity in the x-direction. You then replace the speed by the root mean square speed.
Thanks. Tried to rep but doesn't let me .
17. http://prntscr.com/blbiog

"The weaker candidates focussed on the wording in question concerning elastic collisions. They interpreted this to mean the neutrons maintain their kinetic energy or momentum during all subsequent collisions."

Guess I'm just a weak candidate...

No but seriously can someone explain this?

(June 13 Q2 c) part 2)
18. (Original post by MintyMilk)
http://prntscr.com/blbiog

"The weaker candidates focussed on the wording in question concerning elastic collisions. They interpreted this to mean the neutrons maintain their kinetic energy or momentum during all subsequent collisions."

Guess I'm just a weak candidate...

No but seriously can someone explain this?

(June 13 Q2 c) part 2)
The loss in kinetic energy by the neutron is gained by the moderator, thus Ek is conserved.
19. (Original post by duncant)
The loss in kinetic energy by the neutron is gained by the moderator, thus Ek is conserved.
Oh yeah, of course
20. Predictions on 6 marker for section A and the Applied Physics section?

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