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PHYA5 ~ 20th June 2013 ~ A2 Physics

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Avatar for zbubbly
zbubbly
someone show me how they get 24.7 Mev i got 16.8 , are you not supposed to include the mass of the positrons or something???
Original post by zbubbly
someone show me how they get 24.7 Mev i got 16.8 , are you not supposed to include the mass of the positrons or something???


It wouldnt make that much of a difference if they weren't included. I
Included them but no idea what I got.

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Original post by zbubbly
someone show me how they get 24.7 Mev i got 16.8 , are you not supposed to include the mass of the positrons or something???


the only particle you ignore is the neutrino as they are infinitely small in comparison and therefore their masses are negligible
Original post by zbubbly
someone show me how they get 24.7 Mev i got 16.8 , are you not supposed to include the mass of the positrons or something???


What omega said, you are supposed to ignore the masses of the electrons of the atoms before and after, but all products (things on the right hand, you would include including the positron, just like you would include the neutron as its an product independent of the product atoms.). The neutrino you ignore because I said it has 0 rest mass and the formula book doesn't give its mass :s-smilie:
Reply 1944
Avatar for zbubbly
zbubbly
Original post by jarasta
What omega said, you are supposed to ignore the masses of the electrons of the atoms before and after, but all products (things on the right hand, you would include including the positron, just like you would include the neutron as its an product independent of the product atoms.). The neutrino you ignore because I said it has 0 rest mass and the formula book doesn't give its mass :s-smilie:

well i included the positrons and ignored the neutrinos, still got 16.8, can anyone actually show me the calculation
Original post by zbubbly
well i included the positrons and ignored the neutrinos, still got 16.8, can anyone actually show me the calculation


Helium rest mass (as given in the exam): 4.00150 u

Proton rest mass: 1.00728 u

Positron rest mass: 0.00055 u

(4 x 1.00728)u - (4.00150 + (0.00055 x 2))u = 0.02652u

0.02652 x 931.3 = 24.698076 MeV

∴ 24.7 MeV (3 sf)
Original post by cooldudeman
I think I got like 57 for unit 4 retake and 57 for unit 5. And got 47 for ISA. You lot think it would be enough for an A* considering the difficulties?

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Which option did you take for Unit 5? If you took Turning Points/Medical Physics then I'd say you'd probably comfortably get an A*. Astro and Applied tend to have quite high boundaries and from what I've heard the Astrophysics/Applied papers were quite nice, whereas Turning Points left some people a bit confused so the boundaries will probably be lower.
(edited 10 years ago)
Original post by Technetium
Which option did you take for Unit 5? If you took Turning Points/Medical Physics then I'd say you'd probably comfortably get an A*. Astro and Applied tend to have quite high boundaries and from what I've heard the Astrophysics/Applied papers were quite nice, whereas Turning Points left some people a bit confused so the boundaries will probably be lower.


Yeah I did turning points. I feel like I'm in a threshold position
Original post by cooldudeman
Yeah I did turning points. I feel like I'm in a threshold position


I did Turning Points too! How did you find the paper? I really enjoyed it :h: I think you'll be fine with getting an A* then, normally full UMS is around 61/75.
Reply 1949
Avatar for jimmy_95
jimmy_95
Original post by Tullia
Helium rest mass (as given in the exam): 4.00150 u

Proton rest mass: 1.00728 u

Positron rest mass: 0.00055 u

(4 x 1.00728)u - (4.00150 + (0.00055 x 2))u = 0.02652u

0.02652 x 931.3 = 24.698076 MeV

∴ 24.7 MeV (3 sf)


If i forgot to add the mass of the two poistrons how many marks do you think i will lose. By the way my final answer was 25.7 mev.
Reply 1950
Avatar for jimmy_95
jimmy_95
How do you guys think the ISA grade boundaries will be compared to last years?
Original post by Technetium
I did Turning Points too! How did you find the paper? I really enjoyed it :h: I think you'll be fine with getting an A* then, normally full UMS is around 61/75.


I thought section A was a killer but turning points was smooth. In TP I think I only lost like 5marks. Hopefully I'll get all 6 marks on the standing wave one.

I'm such an idiot for the secA 6marker. I mentioned sealed containers but not tongs or clothing.

Wbu

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Original post by jimmy_95
How do you guys think the ISA grade boundaries will be compared to last years?


Depends how many bastards cheated in those dodgy centres.
Tbh I don't blame them...

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Original post by cooldudeman
I thought section A was a killer but turning points was smooth. In TP I think I only lost like 5marks. Hopefully I'll get all 6 marks on the standing wave one.

I'm such an idiot for the secA 6marker. I mentioned sealed containers but not tongs or clothing.

Wbu

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Section A was weird! They kind of lulled me into a sense of false security with the nice nuclear questions and then BAM.. specific heat capacity calculations :s-smilie:. That TP paper was really nice although the question on showing that the charge of the oil droplet was 1.60x10^-19 was weird, and so was the last question on special relativity.
Reply 1954
Avatar for OJW
OJW
Original post by Tullia
Helium rest mass (as given in the exam): 4.00150 u

Proton rest mass: 1.00728 u

Positron rest mass: 0.00055 u

(4 x 1.00728)u - (4.00150 + (0.00055 x 2))u = 0.02652u

0.02652 x 931.3 = 24.698076 MeV

∴ 24.7 MeV (3 sf)


The formula book said 1u=931.5 MeV so I think I used that, will that make my answer wrong?


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Original post by OJW
The formula book said 1u=931.5 MeV so I think I used that, will that make my answer wrong?


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You'd get exactly the same answer to 3s.f.
Reply 1956
Avatar for OJW
OJW
Original post by OJW
The formula book said 1u=931.5 MeV so I think I used that, will that make my answer wrong?


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Sorry doesn't matter, still 24.7!


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Original post by zbubbly
well i included the positrons and ignored the neutrinos, still got 16.8, can anyone actually show me the calculation
the guy below beat me to it. (above now)
Original post by Technetium
Section A was weird! They kind of lulled me into a sense of false security with the nice nuclear questions and then BAM.. specific heat capacity calculations :s-smilie:. That TP paper was really nice although the question on showing that the charge of the oil droplet was 1.60x10^-19 was weird, and so was the last question on special relativity.


That very last q, I just explained one of the equations and said it would be undefined . it was 2 marks. I think I got one. Fml

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for the "give a source of high radiation from a nuclear power station" I said Uranium 235 would I still get the mark you think?

I needed bang on C for an A and I dont think i even have that :frown:

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