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OCR Physics A G484 Jan 2012 - The Newtonian World

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Reply 160

singh224

Original post by t01

Thanks for this! They're really helpful.

Here's a bunch of questions I have. Some of them are from old spec papers so you can ignore some of them e.g. fission stuff. Includes the answers too.

Also, here's the June 2011 mark scheme and question paper.

I'm loosing marks on all the word'y questions involving thermal physics. I've done all the past papers of this spec so I'm just reading over the book hoping it'll stick in :s-smilie:

Thanks I'll do june 2011 tomorrow got maths exam tomorrow :\

Reply 161

shorty.loves.angels

Can anyone help me out with why F=mrw^2 (where w is angular frequency)

I can't think for the life of me where it comes from or when we might want to use it. Would it be like the tension (force) ... hmm

Oh I found a better breakdown in another book (6 revision books ftw)

So w is angular speed, which = angular displacement (theta) / time (T). When angular displacement is a full circle w=2pi/T so w=2pi*f as f=1/T

Still not sure where we'd use F=mrw^2 though. Anyone able to help?

(edited 12 years ago)

Reply 162

wibletg

Original post by shorty.loves.angels

F = M\frac{v^{2}}{r}

v = rw

F = M\frac {(rw)^{2}}{r}

F = Mrw^{2}

Reply 163

shorty.loves.angels

Original post by wibletg

F = M\frac{v^{2}}{r}

v = rw

F = M\frac {(rw)^{2}}{r}

F = Mrw^{2}

Oh dear why can't I follow that. What's v = rw ... linear velocity?

Reply 164

wibletg

Original post by shorty.loves.angels

Oh dear why can't I follow that. What's v = rw ... linear velocity?

Yep - v = linear velocity, r = radius of circular path, w = angular speed.

If you think about it -

r\theta

= arc length of a circle or linear displacement.

w is rate of change of angle or angular velocity - or

\frac{d\theta}{dt}

So rw is linear velocity. :tongue:

Reply 165

aquark

Original post by shorty.loves.angels

Oh dear why can't I follow that. What's v = rw ... linear velocity?

you can think of it as v=x/t and so v=2 pi r / T
2 pi/T = w therefore v=rw

Reply 166

shorty.loves.angels

Original post by aquark

you can think of it as v=x/t and so v=2 pi r / T
2 pi/T = w therefore v=rw

That was going to be my next question :h:

Cheers for that. Thought I was making good progress today then totally blanked on something so simple!

Reply 167

aquark

Of course wibletg's explanation is equally correct and similar; that type of explanation is often referred to in M3 but not A2 physics.

Original post by shorty.loves.angels

Still not sure where we'd use F=mrw^2 though. Anyone able to help?

Perhaps if you need to solve the equation knowing the period instead of the velocity.

(edited 12 years ago)

Reply 168

username896004

Original post by Jetblast

I shouldn't be awake at this time on a Saturday revising physics, but why does the temperature of a object being heated continue to rise after the source of the heat is taken away?

quote please

the thermal energy has to move from the point of application to the thermometer. This takes time

Reply 169

stunnaman

Original post by Dale12

-Solids- the molecules of a solid vibrate randomly around fixed equilibrium positions. The molecules are closely packed and they exert eclectrical forces on each other.

-Liquids- The molecules of a liquid have translational kinetic energy and they move randomly because of collisions with the other molecules. The mean Separation between the molecules is slightly greater than in the solid state.

-Gases- The molecules have more pronounced random motion and the molecules have translational kinetic energy. The mean kinetic energy increases with temperature. The mean separation between the molecules is much greater than i the liquid state. The molecules exert negligible eclectrical forces on each other, except when they collide.

The kinetic model i has written here is quite detailed, the main thing to remember is about their movement and that liquids and gases have mean translational kinetic energy... the electrostatic forces mentioned should not ever come up in the exam and i doubt they expect you to recall it if mentioned anyway... hope thats helped...

what the hell does translational kinetic energy mean lol...i need a simple definition plz....n this exam doesnt have alot of complex content so i think it shud be easy..mostly gunna be workin out momentum n gravitational attraction definitions questions r easy gud luck evry1 :biggrin:

Reply 170

stunnaman

and ii also think they might ask about geo-staionary orbits..cus i dnt remeber seeing it ona recent past paper :cookie:

Reply 171

stunnaman

Original post by ebmaj7

Anyone know:

Examples of where resonance is a good / bad thing and why?

Examples of where damping is a good / bad thing and why?

resonance is good for tuning intsruments
bad for earthquakes...i.e building will resonate at sme frequency of drivin force

damping a car is good to stop it from vibrating up n down after it hits a speed bumb (elaborte your own words ater..)
bad ..not sure wat for tbh :confused:

Reply 172

wibletg

Original post by ebmaj7

Anyone know:

Examples of where resonance is a good / bad thing and why?

Examples of where damping is a good / bad thing and why?

Resonance -
Good - microwaves, resonates water molecules, cooks food.
Bad - earthquakes. Ground vibrates due to seismic waves leading to collapse of buildings.

Damping -
Good - Car suspension - more comfortable journeys.
Bad - Not a clue to be honest - Pendulums on clocks (?!?!?!) - causes them to stop working.