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# GCSE Physics P3 - 24/05/2012

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1. I left out the minus sign on the 2 calculations with the -1.6 x 10 ^-19

I did this cos i thought you couldn't have a negative kinetic energy, or a negative number of electrons...is this right?
2. Same that's what i did, i left the minus out in front of the equation, because you can't get a negative kinetic energy.
3. I think we're right on those ones.
4. The question for similarities and differences for graph 1 and graph 2?

Describe the graph 4Mv?
5. I left out the minus too
6. There was a question on what happens to the protons neutrons and quarks in positron decay. I also remember there was a question where you had to work out how many seconds one heart beat was and then the beats per minute
7. In B+ decay - happens when there's too little neutrons, so a proton turns into a neutron, and an up-quark turns into a down-quark.

yeah 0.9 seconds from one peak to the next.
8. (Original post by nervouspupil123)
I left out the minus sign on the 2 calculations with the -1.6 x 10 ^-19

I did this cos i thought you couldn't have a negative kinetic energy, or a negative number of electrons...is this right?
I used the minus in the equations, but then when I wrote it in the answer space I left it out and wrote a little note to say you can't have negative kinetic energy.

But now I'm thinking, isn't kinetic energy lost=gravitational potential energy gained, so wouldn't that be a negative KE?
9. When i did the past papers they all excluded the minus sign in the answers (from the mark schemes). But in this case they put a minus infront of the electron volt charge, for the example.
10. Maybe we should ask an alevel physics student?
11. (Original post by Coveted Ul)
The question for similarities and differences for graph 1 and graph 2?

Describe the graph 4Mv?
4mv showed that most of the energy was absorbed by the tissue when it wasn't very deep. As the tissue got deeper, the less energy was absorbed.

I don't know if this is right but for similarities I put that they both absorb some energy overall.
And for the difference i said that the first graph shows that the most energy is absorbed when the tissue isn't very deep whereas the second graph shows that less energy is absorbed when the tissue isn't very deep- but it absorbs the most when the tissue is deep(unlike the X-ray one)
12. What did u guys all do for the thing that was like some weird word like convention something something at the end? Dunno if you understand what i mean haah!!! Do u reckon grade boundaries will be high or low?
13. (Original post by taliaa)
I used the minus in the equations, but then when I wrote it in the answer space I left it out and wrote a little note to say you can't have negative kinetic energy.

But now I'm thinking, isn't kinetic energy lost=gravitational potential energy gained, so wouldn't that be a negative KE?
i let the first answer be negative but the second i made positive.... (can't remember what the questions WERE though)

"kinetic energy cannot be negative. However, a change in kinetic energy can" if that makes sense
14. (Original post by Sugarcandy)
What did u guys all do for the thing that was like some weird word like convention something something at the end? Dunno if you understand what i mean haah!!! Do u reckon grade boundaries will be high or low?
i recon they'll be in the middle because there were some easy questions but there were also some WIERD ones too that i think a lit of people will have not done so well on

what about the one about total internal reflection of ultrasound and the one where you had to draw the x-rays!

(what question are you talking about?)
15. (Original post by Coveted Ul)
How did you guys find the exam? Can we map out the answers?

for the kinetic energy one did you guys put a minus in front of it?
Yes i got a minus infront of the answer for both the kinetic energy question and the number of electrons question as the electronic charge was a MINUS number.
16. For the 2 equations ones involving kinetic energy and Number of electrons, i left the minus at the front IN as if you think about it............the 10 to the minus power bit makes the answer negative but then multiply that it by another MINUS number and it becomes POSITIVE. a negative multiplied by a negative makes a POSITIVE.
17. I found it so hard
18. Could Someone put a mark scheme up .
What did you guys put for the last question . What did someone put for the ECG one ,ultra sound and the graphs.
19. (Original post by umarace)
Could Someone put a mark scheme up .
What did you guys put for the last question . What did someone put for the ECG one ,ultra sound and the graphs.
It was quite difficult but I can't remember what the last question was. Well I dont' have a mark scheme, but for the ultrasound question I put that they need to make sure that the angle of incidence is bigger than the critical angle for total internal reflection to take place. Then for my second point I just put something rubbish that was wrong anyway. I cant remember what the ECG question was. Do u mean the heart rate one? for that my answer was 67 beat per minute
20. I put the same thing for the ultra sound one , I put 75 as the heart beat dunno if its correct and does anyone know all the answers.

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