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# OCR Physics A Breadth of Physics (24th May 2016) Discussion

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1. (Original post by richpanda)

Denisty was 7500kgm^-3, not 750kgm^-3 as some peolle have suggested- how can a metal cylinder be less dense than water, considering it sank in the water?

Drift velocity was something like 1.7 x 10^-3. Lots of you probably forgot to find the number density (number per m^3) and just used the number of electrons they gave you (incorrect)

Momentum- 70 or 80ish for the velocity of the carbon atom.

Rest of the questions were pretty standard.
I remember getting that I couldn't remember if it was 10^-4 or 3 :P for the drift velocity. Considering electrons travel slowly it made sense.
2. (Original post by spaceman11)
I subbed the values from the graph into the equation and got a to be 7.6...?
(Original post by isaac_wood_)
Yeah the gradient was 16 but that was equal to 2a as u^2/x = 2a, so a = 8 (I think)
I got 7.6 but then I looked at the graph again using more clear points and got a=8 exactly. Then it was just f=ma.
3. What were the two conserved physical quantities in the inelastic collision (comet or whatever)? I think it was 1 mark, i knew momentum was one, I didn't put kintetic energy because its not conserved in inelastic collisions, so randomly put mass lol. I heard someone say it was momentum and total energy is that right?
4. Worst paper ever!! Didnt even have time to finish the last question
5. (Original post by JAFF2400)
What were the two conserved physical quantities in the inelastic collision (comet or whatever)? I think it was 1 mark, i knew momentum was one, I didn't put kintetic energy because its not conserved in inelastic collisions, so randomly put mass lol. I heard someone say it was momentum and total energy is that right?
Yes total energy in the system, by the way what did people write about how the calculation of adding mass was different to velocity. Did you just have to say one was a vector, the other scalar therefore when adding velocity you have to count for direction aswell.
6. (Original post by JAFF2400)
What were the two conserved physical quantities in the inelastic collision (comet or whatever)? I think it was 1 mark, i knew momentum was one, I didn't put kintetic energy because its not conserved in inelastic collisions, so randomly put mass lol. I heard someone say it was momentum and total energy is that right?
It's definitely not energy because the collision was inelastic.
And I'm not sure what the second was but I also put mass
7. what did people get for the last question? I got 2.9 x 10^16 (i cant remember if that was the power but I definitely got 2.9)
8. (Original post by flamingllama)
It's definitely not energy because the collision was inelastic.
And I'm not sure what the second was but I also put mass
Total energy and momentum.
9. (Original post by flamingllama)
It's definitely not energy because the collision was inelastic.
And I'm not sure what the second was but I also put mass
I thought it was total energy, because of the conservation of energy means
energy in =energy out just in different forms. Can anyone confirm??
10. (Original post by flamingllama)
It's definitely not energy because the collision was inelastic.
And I'm not sure what the second was but I also put mass
Inelastic just means KINETIC energy isn't conserved, but the total energy is conserved

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11. (Original post by _Orion_)
Inelastic just means KINETIC energy isn't conserved, but the total energy is conserved

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someone upload unofficial mark scheme pls
12. which point the ball reach the maximun
13. (Original post by chenhao96)
which point the ball reach the maximun
I put C :/ i dunno though ive ****ed up the whole paper
14. (Original post by flamingllama)
what did people get for the last question? I got 2.9 x 10^16 (i cant remember if that was the power but I definitely got 2.9)
I got this too
15. (Original post by santos668)
1 for R and 2R
But P=V^2/R, the V is the same for both as they are in parallel and one has double the resistance so it can't be 1 can it?
16. (Original post by chenhao96)
which point the ball reach the maximun
D i think
17. (Original post by flamingllama)
what did people get for the last question? I got 2.9 x 10^16 (i cant remember if that was the power but I definitely got 2.9)
how?
18. (Original post by viktorh)
what did people get for the multiple choice question about the power output over x and y with the two resistors in series? I guessed 28mW after coming up with 0.003 watts with all my calculations
i got 12 mW, because energy is conserved at a junction, the power dissipated by the resistor was 12mW.
19. (Original post by maryamkhawaja)
D i think
I think it was C because when it crossed the zero line again that means is accelerating towards the ground and at D it hit the ground
20. (Original post by ZacS)
I think it was C because when it crossed the zero line again that means is accelerating towards the ground and at D it hit the ground
it said max displ after it bounces once.

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