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AQA A Physics Unit 4 24th Jan 2012

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Reply 120

lee_vassallo

Thanks dude, you make it look so easy :tongue:

Reply 121

spoinkytheduck

Hii physics people!! :biggrin:

Major stressing over this exam... A2 feels wayy harder than last year :s-smilie:

I was wondering if anyone had something like a 'key facts' document or something..?? I'm just trying to find something that summarises the really inportant bits into bullet points or short sections... everything I'm finding seems to just have about 30 pages full of long-winded explanations! :tongue:

Thanks

Reply 122

schizopear

on the specification under simple harmonic motion it says "variation of Ek, Ep and total energy with displacement, and with time". what would the variation with time be?

Reply 123

Femto

Original post by schizopear

on the specification under simple harmonic motion it says "variation of Ek, Ep and total energy with displacement, and with time". what would the variation with time be?

I answered a question incorrectly earlier in this thread relating to energy against time.

Well, kinetic energy as I'm sure you are aware of is

\dfrac{1}{2}mv^2

. Since

v = \pm 2\pi f \sqrt{A^2 - x^2}

, with some fiddling around, you end up with:

E_k = 2m\pi^2f^2A^2\sin^2 (2\pi ft)

So, this yields that:

E_k \propto \sin^2 (\omega t)

You can similarly deduce that:

E_p \propto \cos^2 (\omega t)

So when you're trying to sketch kinetic energy against time for instance, just draw a graph which resembles

y = \sin^2 (x)

Reply 124

handsome7654

Original post by Femto

I answered a question incorrectly earlier in this thread relating to energy against time.

Well, kinetic energy as I'm sure you are aware of is

\dfrac{1}{2}mv^2

. Since

v = \pm 2\pi f \sqrt{A^2 - x^2}

, with some fiddling around, you end up with:

E_k = 2m\pi^2f^2A^2\sin^2 (2\pi ft)

So, this yields that:

E_k \propto \sin^2 (\omega t)

You can similarly deduce that:

E_p \propto \cos^2 (\omega t)

So when you're trying to sketch kinetic energy against time for instance, just draw a graph which resembles

y = \sin^2 (x)

Thankyou!

I understand how you got to

E_k = 2m\pi^2f^2A^2\sin^2 (2\pi ft)

which led you to conclude that

E_k \propto \sin^2 (\omega t)

since the constant k = 2m(pifA)^2
But how did u figure out that

E_p \propto \cos^2 (\omega t)

Reply 125

jones_wise

Is electric potential a scalar or vector quantity?

Reply 126

don'tTRIP.

Original post by jones_wise

Is electric potential a scalar or vector quantity?

Scalar

Reply 127

jones_wise

Original post by don'tTRIP.

Scalar

Thank you!

Reply 128

Legendary

No horsepower questions and this should hopefully be a ok paper considering AQA have made papers much harder so far this Jan.

Reply 129

m1a1tank

I have a question about circular motion.

For a particle moving in a circle with uniform speed, why is it's kinetic energy constant but its momentum is not?

Reply 130

Legendary

Original post by m1a1tank

I have a question about circular motion.

For a particle moving in a circle with uniform speed, why is it's kinetic energy constant but its momentum is not?

I was wondering that too the other day decided to do the chapter again and found that speed is constant but velocity isn't therefore momentum isn't.

Reply 131

kimmey

Original post by m1a1tank

I have a question about circular motion.

For a particle moving in a circle with uniform speed, why is it's kinetic energy constant but its momentum is not?

momentum is a vector but kinetic energy is a scalar

v is constantly changing but the speed is constant :smile:

thanks

Aaargh, I am so not ready for this exam. I've been going through the book revising, and we did a past paper on tuesday in lesson which our teacher marked, and I only got 40% on multiple choice, and even less on the written. I revise things, and understand things when i'm revising but I just confuse things between topics, and I don't know what equations go with what topic, especially the ones not on the formula sheet. And if the 6 mark question is on SHM I will just get up and walk out the room.

Reply 134

paul.dirac121

hey comrads. has anyone done the isa this year on damped oscillations in a u shaped water column? we have it this monday. really need help

Reply 135

arnab

Original post by manyin

http://www.physicsteachers.com/pdf/AQA%20past%20papers/Unit%204/AQA-PHYA4-W-MS-Jun11.pdf

that is the mark scheme for jun 2011 unit 4

have u got the paper?

Reply 136

npaul4

Original post by Quornslice

I know exactly how you feel, we had a mock test recently and i got a U!! I generally undersand the individual units but once they're altogether in a paper I just get so confused :s-smilie:

Reply 137