OCR Physics A G484 Jan 2012 - The Newtonian World

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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?

This is what i did .. I put a cross where the displacement for the graph was zero .. but i did not put the cross on the X axis do you think they will mark me down for me .. have a look at the picture to get a better understanding

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Reply 881

just george

Original post by DavidMRoper

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!

Do you think you could show your workings out to get that? i didnt really know how to do it and improvised and got around 3.4W :L

Reply 882

wig44

Original post by just george

Do you think you could show your workings out to get that? i didnt really know how to do it and improvised and got around 3.4W :L

You assumed velocity was always vmax, which is incorrect.

Reply 883

just george

Original post by wig44

You assumed velocity was always vmax, which is incorrect.

Thanks, i assumed that was wrong, but surely in that case the answer would have to be less than 3.4W as the mean velocity would have to be lower than Vmax..

edit: but actually surely mean velocity = 0 as its a vector quanity, so my calculation would get P = 0? now im confused :tongue:

(edited 12 years ago)

Reply 884

Tempzzz

Paper went alright, praying i scrape a B at least.

Missed out the power question of the cone, and stupidly instead of finding acceleration of cone, i mis-read and found of max velocity FML!! For the greenhouse question i got temperature increase as 2.42, but converted it to Kelvins when I shouldn't have loool

Other than that it went kinda ok ...

What did people get for the mass of the hydrogen atom? I got 3x10 ^ -27 kg

Reply 885

username896004

Original post by just george

Do you think you could show your workings out to get that? i didnt really know how to do it and improvised and got around 3.4W :L

It's quite simple.
In one oscillation, the mass travels 4 times the amplitude.
Times that by force
Times that by frequency.

I only did 2 times displacement- FACEPALM

Reply 886

Megatron94

Original post by H_Rattan

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!

I wrote something like that too, how some molecules collide with each other and ones with kinetic energy would be able to leave

Reply 887

EW11

A silly question... anybody else forget how to convert something into MEGA something?!!!

Reply 888

UnknownPerson

Original post by unknownperson

this is what i did .. I put a cross where the displacement for the graph was zero .. But i did not put the cross on the x axis do you think they will mark me down for me .. Have a look at the picture to get a better understanding

someone answer my ques

Reply 889

rawr4more

For the last questions i checked wid my teacher its that cuz u have that equation thats like 1/3pc^2 or summin n cuz C is an average speed other molecules have different speeds. Sorry for bad spellin im on ze iphone xD

Reply 890

Megatron94

Original post by EW11

A silly question... anybody else forget how to convert something into MEGA something?!!!

wouldnt that be /10^6

Reply 891

just george

Original post by DavidMRoper

It's quite simple.
In one oscillation, the mass travels 4 times the amplitude.
Times that by force
Times that by frequency.

I only did 2 times displacement- FACEPALM

Hmm, i understand what youv done, that makes sense and is probably what they were wanting.. but im still not sure how the answer can be greater than mine, unless something in my workings is wrong before the point "Fv/2 = P"? because me using Vmax would get a value for P greater than it should be surely?

Reply 892

UnknownPerson

Original post by teachercol

Sometimes the examiners just set stupid questions - and sometimes the mark schemes are equally stupid.

For the simple harmonic question where it asked us to put a cross where the velocity was maximum .. it put a cross where the displacement for the graph was '0'. However, i didnt put the cross on the x axis do you think they can mark me down for it .. ive taken a picture of how i did it .. have a look at it and tell me if i wud lose a mark of not .. Have a look at the picture .. ive put the cross higher up do you think i will get a mark

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Reply 893

Pooey

Original post by EW11

A silly question... anybody else forget how to convert something into MEGA something?!!!

Lol haha, yeah I would be one who did :P

Reply 894

Stevo F

Original post by UnknownPerson

someone answer my ques

theres no way of knowing i'm afraid, u'll just have to wait for the results for that one ^^

Reply 895

Pooey

What did people put down for the question that asked you to state two reasons why the temperature change may not be as high... it was that greenhouse question.

Reply 896

perrytheplatypus

Did anyone write, for the geostationary orbit one, that it's above the equator so it can transmit to anywhere in the world? Because if it was too up north, it wouldn't be able to transmit to the south due to the curvature of the earth.

Sounds stupid, but I had no idea about the answer.

Reply 897

Centurion16

What did you have to do with the question about the force and power (damping question). What actually did you have to find, the questions are starting to jumble in my head :/

Reply 898

PeterStoba

Felt it was a good paper.

Think I've dropped quite a few marks though from silly mistakes. Didn't like that question about the loudspeaker cone (Think I've done Vmax not a) part ii was hard aswell, didn't have a clue.

Also dropped marks on the Why is the greenhouse temperature not as high one, the Helium escape velocity and geostationary orbits at the equator. Hoping for a B anyway

Reply 899

Gould1610

Anybody else multiply the force by the frequency by 4 times the amplitude and get 4.32 W??

Please say somebody did as above :P

And i can't remember if it was 18mm or 1.8mm in the question about the speaker now, anybody remember that?