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OCR Physics A G484 Jan 2012 - The Newtonian World

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Reply 860
Original post by Stevo F
nope potential energy is lowest when distance from equilibrium is lowest


yeah i just understood - its swinging....no way there's another mark i've lost....i thought it was a decent paper....but stupid mistakes are going to pull my grade down :frown:
anyone know how to do the damping question though, my method was a bit odd and probably wrong :L i did:

p=e/t

e=(mv^2)/2

so p=(mv^2)/2t

f=ma = mv/t

so fv/2 = (mv^2)/2t = p

so 0.25v/2 = p

and then i didnt know how to find the mean velocity so used Vmax and substituted that in :L ended up with something like 3.4W
Original post by Stevo F
min P.E is when displacement=0 sorry
Ur thinking of energy as being positive or negative but you can't have negative energy :smile:


Thanks I just realised :biggrin:
Reply 863
Original post by just george
anyone know how to do the damping question though, my method was a bit odd and probably wrong :L i did:

p=e/t

e=(mv^2)/2

so p=(mv^2)/2t

f=ma = mv/t

so fv/2 = (mv^2)/2t = p

so 0.25v/2 = p

and then i didnt know how to find the mean velocity so used Vmax and substituted that in :L ended up with something like 3.4W


Well its the right answer i think so probs full marks
it's so rude that they keep slipping power questions into papers and i just have no idea how to deal with them :frown:
Is P=Fv the right way to go about answering that question which involved 0.25N?
Reply 866
Original post by teachercol
I have a job teaching A level Physics too :wink:


I didn't mean to come across as rude in my post, obviously you posting solutions is a liberty and not a right to be expected!
Original post by Stevo F
Well its the right answer i think so probs full marks


cheers mate, maths improvisation ftw :tongue:
I wrote the wrong word in Kepler's law and by the time I'd crossed it out there was hardly any room left so I'm not even sure my answer is legible :facepalm:

For that escape velocity... I talked about kinetic energy/ velocity or something about how some would have higher velocity blah blah. Was I at least along the right lines?
Original post by shorty.loves.angels
I wrote the wrong word in Kepler's law and by the time I'd crossed it out there was hardly any room left so I'm not even sure my answer is legible :facepalm:

For that escape velocity... I talked about kinetic energy/ velocity or something about how some would have higher velocity blah blah. Was I at least along the right lines?


i completely forgot keplers law :L oh well..

i think for the escape velocity q: 2.5kms^-1 was the average velocity. so some atoms will travel slower than that, and some will travel faster. The ones travelling faster than 11kms^1 would escape
Reply 870
Original post by shorty.loves.angels
I wrote the wrong word in Kepler's law and by the time I'd crossed it out there was hardly any room left so I'm not even sure my answer is legible :facepalm:

For that escape velocity... I talked about kinetic energy/ velocity or something about how some would have higher velocity blah blah. Was I at least along the right lines?


for the escape velocity i wrote that because of the random collisions of gas molecules..some atoms would have higher energies than others - and therefore some may have a velocity thats higher than the escape velocity....no idea if thats right, just throwing my answer out there!
Reply 871
Do you think that grade boundries will be higher as we had more time than previous papers? Or do you not think that will made a difference to the boundries...
I am confused about the SHM motion .. we were are to put 'X' at point where the velocity was max and the acceleration was zero .. Were they not asking us the Time at which it would have maximum velocity rather than the displacement at which it would be maximum or minimum ???
(edited 12 years ago)
Reply 873
Cant see grade boundaries being like last year, dropping 16 marks and still getting an A on this paper...not sure! Realised I did make a fair few silly mistakes after reading here, there goes my A* :frown:

For the last question, could it be due to the helium being less dense than the air molecules, hence naturally the helium molecules would rise to/above the atmosphere of the earth allowing them to escape?

A quick Google search found this to be correct...if this is what they are looking for however i do not know.
Original post by DrMute
Cant see grade boundaries being like last year, dropping 16 marks and still getting an A on this paper...not sure! Realised I did make a fair few silly mistakes after reading here, there goes my A* :frown:

For the last question, could it be due to the helium being less dense than the air molecules, hence naturally the helium molecules would rise to/above the atmosphere of the earth allowing them to escape?

A quick Google search found this to be correct...if this is what they are looking for however i do not know.


Hmm i doubt that is what they are looking for im afraid. They stated that the average velocity of helium atoms was 2.5kms^1, and that to escape an atom needs to be travelling faster than 11kms^1 so i think they were wanting you to pick out the fact that its an 'average' velocity so some of the helium atoms would escape
Reply 875
Original post by DrMute
Cant see grade boundaries being like last year, dropping 16 marks and still getting an A on this paper...not sure! Realised I did make a fair few silly mistakes after reading here, there goes my A* :frown:

For the last question, could it be due to the helium being less dense than the air molecules, hence naturally the helium molecules would rise to/above the atmosphere of the earth allowing them to escape?

A quick Google search found this to be correct...if this is what they are looking for however i do not know.


obviously its correct, why else would you put helium in your balloons? lol
I made another statement which is also correct too and I also dont know if it'll be credited with any marks :smile:
Original post by UnknownPerson
I am confused about the SHM motion .. we were are to put 'X' at point where the velocity was max and the acceleration was zero .. Were they not asking us the Time at which it would have maximum velocity rather than the displacement at which it would be maximum or minimum ???


Vmax = when displacement is 0 (i.e. equilibrium point)

acceleration is 0 = when displacement is 0 (i.e. equilibrium point)

Potential energy is minimum = when displacement is 0 (i.e. equilibrium point)


I think for the Vmax one it would have to be an equilibrium point going from -ve to +ve though otherwise it would be Vmin?
i think theres going to be some really high grade boundries for this exam..
for the last question, isnt it just to do with the weight? He is lighter than most other molecules
The unfunny moment when your mates tell you there was a 8 mark question 7 you missed. Not so funny when you have OCD, cried and ran off somewhere in the night to have your mum pick you up in a car. It's okay I'm calm- chilled, and I've worked out the power one was actually 4.32 sorry for my earlier statement of 2.16!

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