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

Reply 900

Tazmain

8

Original post by AlexParmenter

In the textbook is says molecules in steam have far greater random potential energy than those in boiling water :frown:

Also if the curve is energy against temperature, and the temperature isn't increasing, the substance is still absorbing heat so that heat would be used to increase the potential energy

What we were taught is potential energy does increase from solid to liquid to gas. Water is a weird case because the solid lattice structure is less dense than liquid, so for ice changing into liquid water, potential energy decreases. When water becomes steam, potential energy increases as work is done to break hydrogen bonds, so the molecules are further apart, increasing their "potential" energy.

Ideal gases on the other hand have no potential energy, that's because we assume they have no intermolecular forces between molecules.

So, with the exception of water, and an ideal gas, potential energy increases from solid, to liquid and to gas.

Reply 901

Alex621

17

Original post by Tazmain

What we were taught is potential energy does increase from solid to liquid to gas. Water is a weird case because the solid lattice structure is less dense than liquid, so for ice changing into liquid water, potential energy decreases. When water becomes steam, potential energy increases as work is done to break hydrogen bonds, so the molecules are further apart, increasing their "potential" energy.

Ideal gases on the other hand have no potential energy, that's because we assume they have no intermolecular forces between molecules.

So, with the exception of water, and an ideal gas, potential energy increases from solid, to liquid and to gas.

That's what I was taught too, maybe everyone was talking about ideal gases, sorry it just seemed like people were saying the opposite of what I thought was right :redface:

Reply 902

sagar448

4

I don't have a good feeling about this exam... I hope it's like last year's exam; with some hard questions and a lower grade boundary for an A*. :C

Reply 903

Raizel

3

Density = m/v --> PV=nRT ---> n=1
mark schemes says that if n=1 then m=M
why?

Original post by Raizel

Guys can someone go explain why it is (m/M) for question 6c on the june 2014 paper https://drive.google.com/folderview?id=0B1ZiqBksUHNYfnBrUUlyc0Rfdm8tekpIUFZ4cGZicEpwd25jYUNLZ3c2NG9WRDZRa2dJQkE#

mass / molar mass = number of moles

Reply 905

FeelsToWaltz

2

Original post by Makashima

in shm motion, one oscillation is actually 1/4 of the time period?

No the time period is the time for one oscillation. You might be thinking about the amplitude being a 1/4 of the distance traveled in one oscillation.

Reply 906

Raizel

3

Original post by Username13

mass / molar mass = number of moles

Thanks m8.

Reply 907

Makashima

16

Original post by FeelsToWaltz

No the time period is the time for one oscillation. You might be thinking about the amplitude being a 1/4 of the distance traveled in one oscillation.

ah yea, prob
just remember some question idk which
but it was like you need to mutiple by four because the period was 1/4 hmm ill look for it

Reply 908

giantbecky

8

Do people think there is literally no chance SHC experiment will come up again since it came up last year??

Reply 909

Alex621

17

Original post by Makashima

ah yea, prob
just remember some question idk which
but it was like you need to mutiple by four because the period was 1/4 hmm ill look for it

Might be jan 12 paper, just did it and it had a question which sounds like the one you're talking about

Reply 910

coder4

2

Can anyone clarify the significant figures required? Max 2 or 3? Any more and you lose a mark am I right? Just checking

Reply 911

Jmw123

3

Anyone have last years paper and mark scheme?

Reply 912

seizetoday

12

How can you describe the acceleration of an object from a Force Time graph?

Reply 913

seizetoday

12

Original post by coder4

Can anyone clarify the significant figures required? Max 2 or 3? Any more and you lose a mark am I right? Just checking

You won't lose any marks if you quote it to 2 or 3 significant figures. 2 is preferred.
Any more than 3 you will probs get penalised 1 mark

Reply 914

seizetoday

12

Original post by giantbecky

Do people think there is literally no chance SHC experiment will come up again since it came up last year??

There is always a chance.

Reply 915

randlemcmurphy

11

Original post by seizetoday

How can you describe the acceleration of an object from a Force Time graph?

I'd like some clarification on this as well.

Reply 916

sagar448

4

Original post by randlemcmurphy

I'd like some clarification on this as well.

Well basically, three things could happen to a force on the graph and i'l go over that...

Force increases - since force is increasing the object is accelerating faster!
force constant - since force is constant the objects is still accelerating but constantly..
force decreases - since force is decreasing the object is still accelerating but at a decreasing rate (THIS IS NOT DECELERATION)

Thats about it really. :biggrin:

Reply 917

rachelc142

11

Original post by seizetoday

How can you describe the acceleration of an object from a Force Time graph?

Original post by randlemcmurphy

I'd like some clarification on this as well.

the gradient of the graph is proportional to the change in momentum
so if the grad is flat then the change in momentum is constant ie it is uniformly accelerating
if the grad is non flat/sloped then the change in momentum is increasing/decreasing so it is non uniformly accelerating :-)

(edited 8 years ago)

Reply 918

randlemcmurphy

11

Original post by sagar448

Well basically, three things could happen to a force on the graph and i'l go over that...

Force increases - since force is increasing the object is accelerating faster!
force constant - since force is constant the objects is still accelerating but constantly..
force decreases - since force is decreasing the object is still accelerating but at a decreasing rate (THIS IS NOT DECELERATION)

Thats about it really. :biggrin:

Thanks. I'll rep you when I can :3