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OCR Physics A G484 - The Newtonian World - 11th June 2015

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Newtons 2nd law says that the rate of change of momentum is proportional to the resultant force and in the same direction as the resultant force. So if a particle was travelling towards the right and then collided elastically with a wall and rebounded, wouldn't that mean that the particle has a negative change in momentum? So wouldn't the resultant force be acting to the left because of the negative change in momentum, shouldn't it actually be to the right? What's wrong with my logic
(edited 8 years ago)
Original post by BrokenS0ulz
Newtons 2nd law says that the rate of change of momentum is proportional to the resultant force and in the same direction as the resultant force. So if a particle was travelling towards the right and then collided elastically with a wall and rebounded, wouldn't that mean that the particle has a negative change in momentum? So wouldn't the resultant force be acting to the left because of the negative change in momentum, shouldn't it actually be to the right? What's wrong with my logic


If we take the left to be the positive direction then the change in momentum would be mv -(-mv) = 2mv, the force acting on the particle from the wall would be to the left, so is also in the positive direction.
(edited 8 years ago)
Original post by Mr_Cupcakes
If we take the left to be the positive direction then the change in momentum would be mv -(-mv) = 2mv, the force acting on the particle from the wall would be to the left, so is also in the positive direction.


But isn't the resultant force due to the particle on the wall to the right?
is this correct, some please check

internal energy = 3/2kT = 1/2mv^2

if temperature was to halve, then u would also halve too thus u/2 because 3/2 and k is constant

t is proportional to v^2
so t/2 will make (v^2)/2
so velocity will decrease by a what? square root half?

my maths is very bad lulz, thanks
(edited 8 years ago)
Original post by Makashima
is this correct, some please check

internal energy = 3/2kT = 1/2mv^2

if temperature was to halve, then u would also halve too thus u/2 because 3/2 and k is constant

t is proportional to v^2
so t/2 will make (v^2)/2
so velocity will decrease by a factor of four?

my maths is very bad lulz, thanks


T prop v²
As an example, put numbers in T=100,v=20

100 = 400k
k = 1/4

T=50
50 = 1/4 v²
v = root200
v = 14 ish

So as you can see not a quarter

It decreases by a root of 2
Original post by L'Evil Fish
T prop v²
As an example, put numbers in T=100,v=20

100 = 400k
k = 1/4

T=50
50 = 1/4 v²
v = root200
v = 14 ish

So as you can see not a quarter

It decreases by a root of 2


thanks :smile:
What's everyone learnt for "describe using a simple kinetic model for matter the terms melting, boiling and evaporation"?
Original post by BrokenS0ulz
What's everyone learnt for "describe using a simple kinetic model for matter the terms melting, boiling and evaporation"?


Just variations in internal, kinetic and potential energies and effects on particles:

Melting:
>Solid heats up, particles vibrate more frequently so more collisions.
>KE rises
>LHM indicates atomic bonds break up and particles move more freely
>potential energies rise
>internal energies rise

Boiling:
>particles are further apart so more energy is required to reach LHV
>KE rises as temperature rises
>LHV splitting bonds again
>PE rises
>internal energy rises

Post-Evaporation:
>particles are fast-moving
>highest KE and PE
>even further distances apart

That's what I think anyway:redface:
Hope this helped

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Can anyone explain Jan 2012 2cii to me
SO you know the damping force=0.25N

1. Power=energy/time
2. Energy required to overcome the dampening force= 0.25 x 1.8x10^-3 x 4=1.8x10^-3(Joules)
3.work out time period of oscillation= T=1/f=1/2.4x10^3=4.17x10^-4 s

4. Power= energy/time=1.8x10^-3/4.17x10^-4=4.32 W
Anyone do it G482, how did it compare to other years?
Original post by chem@uni
Anyone do it G482, how did it compare to other years?


^ Just tagged sagar448 as I know he did.
Original post by chem@uni
Anyone do it G482, how did it compare to other years?


Original post by randlemcmurphy
^ Just tagged sagar448 as I know he did.


I wouldn't say it was hard, but it was definitely tricky. They had like a few things you needed to remember to include in the calculations or you'd mess up. All in all I think it was OK, i'm guessing the grade boundaries will be similar to last year, if not higher. So for G484/5 I think prepare as much as you can, because you never know. OCR is one ****ed up exam board. Their format is never the same, they just literally put in whatever bull**** they want. I think i did alright, definitely higher than last year. :biggrin:
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Original post by chem@uni
Anyone do it G482, how did it compare to other years?


Yeh i did a resit, i thought it went okay but nobody else is giving that signal, everyone in my school hated it and everyone on here hated it?
I did a day revision if that so probably the fact i have a lot more confidence now would be why i thought it went okay, either way hard paper but doable
What examples of practicals do they think they could ask us to describe ? (4-6 marks maybe)

The ones I could think of are:
-pendulum bob
-bung on a string
-specific heat capacity
-resonance and damping
-brownian motion smoke cell
-boyle's law with the oil and pressure gauge

Can anyone think of any others?
Thanks!
Original post by ReeceG46
What examples of practicals do they think they could ask us to describe ? (4-6 marks maybe)

The ones I could think of are:
-pendulum bob
-bung on a string
-specific heat capacity
-resonance and damping
-brownian motion smoke cell
-boyle's law with the oil and pressure gauge

Can anyone think of any others?
Thanks!


Obtaining a cooling curve possibly.
How to have a life

Posted from TSR Mobile
Original post by randlemcmurphy
Obtaining a cooling curve possibly.


I'm not sure about the practicals for the resonance and damping, boyles and brownian. Mind running through them quickly? And the cooling curve?

Thanks :3
Original post by sagar448
I'm not sure about the practicals for the resonance and damping, boyles and brownian. Mind running through them quickly? And the cooling curve?

Thanks :3


I've just come across these from revision guides and things:
1) damping and resonance, attach a mass with a spring on the end to some sort of signal generator that can cause the spring and mass to oscillate vertically. Behind the spring , have a ruler or some measuring device. Increase the frequency of the signal generator until you get the maximum amplitude of oscillation (by looking at the ruler) this frequency is the natural resonant frequency of the mass/spring system. Repeat this but place the mass in a beaker of water. Observe the max amplitude and natural frequency both decrease due to damping.

2) for Brownian motion, have a glass smoke cell placed under a microscope, use a filament or some other light source to illuminate the glass jar. Observe the motion through the microscope. The smoke particles appear as tiny specs of light. Then talk about the conclusions you can make about the gas

3) boyle's law, have a closed cylinder containing a fixed mass of air and some oil. Using a foot pump and pressure meter, increase the pressure of the air in the column and read off the corresponding volume of oil ( the height of the oil will change) then for ech set of values calculate pressure x volume, which should remain constant.

Not sure about the cooling curve , sorry
Original post by ReeceG46
...


Original post by sagar448
...


(https://b1a3c7824d6ff508e2bd2668b57bcac540764bbe.googledrive.com/host/0B1ZiqBksUHNYa1dha1BqWUwyanc/Detailed-Notes-with-Questions/4.3.1%20Solid%20%20Liquid%20and%20Gas.pdf)
Page 7 for the cooling curve practical.

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