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# Edexcel A2 Physics Unit 5 'Physics from Creation to Collapse' watch

1. (Original post by dana.h)
now its perfect .. another question how do i know when to use cos or sin for getting displacement?
If they give you a graph - from that. Or if they give you acc/velocity graphs:

velocity sine = displacement and acceleration cosine

velocity cosine = displacement + acceleration sine

2. (Original post by dana.h)
now its perfect .. another question how do i know when to use cos or sin for getting displacement?
always use cos 4 displacement..sin for velocity ,cos for acceleration.
3. does anyone have a formula sheet please, which ones are we supposed to memorise\?
4. (Original post by nnamdi)
always use cos 4 displacement..sin for velocity ,cos for acceleration.
no, that's wrong, we use sin and cos depending on the starting position of the oscillating object.
For instance, if it starts at its max displacement ( amplitude ), we use cos for x, however if it starts at its min displacement, we use sin for x.
then we can find the velocity by differentiating the equation of x, and acceleration by differentiating the equation of v..

Good luck everyone
5 and a half hours left!
5. (Original post by dimi3)
could someone explain the displacement-time graph for an overdamped object? I dont get why the displacement does not go all the way to zero
the oscillation stops before going through its equilibrium position, that's why its graph looks like that!
and btw after a very long period of time, it might reach a displacement of zero!
6. (Original post by kosy91)
edexcel blue book. page 188 . about astronomical distances

in thw worked example, we have been asked to find distance of the star from the earth. so why have they given distance between sun and the star??? surely its NOT the same thing!!
I don't have the book, but it is right.

Using the parallax method, you always calculate the distance from the star to the Sun. I have no idea why. I guess cause the Sun never moves?
7. I just wish if they don't get us anything related to the AS
8. (Original post by Bronze92)
the oscillation stops before going through its equilibrium position, that's why its graph looks like that!
and btw after a very long period of time, it might reach a displacement of zero!
sorry i dont get it! when you say it stops before going through its equilibrium position, what exactly do we take to be the equilibrium position?
this second question will probably explain itself if i get the first one but what do you mean it might reach a displacement of zero? (an example would probably help)
9. (Original post by Bronze92)
I just wish if they don't get us anything related to the AS
I wish the exam was something along the lines of:
you open the paper, and there's nothing.

But, seriously, the only hard AS thing they could give us is materials.
10. okay guys. i have this question can someone tell me how to use distances like the relations... for example i know 1 parsec equals to 3.26 light years what about other relations?
11. (Original post by dimi3)
sorry i dont get it! when you say it stops before going through its equilibrium position, what exactly do we take to be the equilibrium position?
this second question will probably explain itself if i get the first one but what do you mean it might reach a displacement of zero? (an example would probably help)
imagine a car suspension system, over damping would help stop the oscillation of the system without reaching it's equilibrium position!
however, over a longer period of time, the object might return to its initial position (when the restoring force = 0)
12. (Original post by dana.h)
okay guys. i have this question can someone tell me how to use distances like the relations... for example i know 1 parsec equals to 3.26 light years what about other relations?
http://www.wolframalpha.com/input/?i=parsec
13. (Original post by Bronze92)
no, that's wrong, we use sin and cos depending on the starting position of the oscillating object.
For instance, if it starts at its max displacement ( amplitude ), we use cos for x, however if it starts at its min displacement, we use sin for x.
then we can find the velocity by differentiating the equation of x, and acceleration by differentiating the equation of v..

Good luck everyone
5 and a half hours left!
WHAT????????????
cud u plz do with a little bit of more explanation cuz all this time i have been using cos for displacement and acceleration and sine for velocity!!!!
Thnx
14. Ahhhh I am so freaked out by this test to day. I haven't been nervous for any of the others.

In the sample paper last night I got 65%, which is only a C really, right?

I wonder if I do really well in everything else, if it's possible to still get a B?
15. (Original post by terminatorsb)
WHAT????????????
cud u plz do with a little bit of more explanation cuz all this time i have been using cos for displacement and acceleration and sine for velocity!!!!
Thnx
it all depends on the starting position!!!
just draw a graph of displacement time graph, for instance if it starts its motion at the amplitude, it would be a cosine graph, so x = A cos (wt)
and v is x's derivative.

Good luck
16. (Original post by terminatorsb)
WHAT????????????
cud u plz do with a little bit of more explanation cuz all this time i have been using cos for displacement and acceleration and sine for velocity!!!!
Thnx

okay so if the oscillation is starting at maximum which is the extreme point then for calculating displacement you should use cos and then differeniate to get the velocity and acceleration
if in the question its mentioned that it starts from mean position which is the equilibrium position you have to use sin for the displacement and depending on that differentiate for velocity and aceleration
17. can someone explain the example on pg 188 about the centauri
18. (Original post by Bronze92)
it all depends on the starting position!!!
just draw a graph of displacement time graph, for instance if it starts its motion at the amplitude, it would be a cosine graph, so x = A cos (wt)
and v is x's derivative.

Good luck
Thank you!!
19. (Original post by dana.h)
okay so if the oscillation is starting at maximum which is the extreme point then for calculating displacement you should use cos and then differeniate to get the velocity and acceleration
if in the question its mentioned that it starts from mean position which is the equilibrium position you have to use sin for the displacement and depending on that differentiate for velocity and aceleration
Thank you!!
20. (Original post by terminatorsb)
WHAT????????????
cud u plz do with a little bit of more explanation cuz all this time i have been using cos for displacement and acceleration and sine for velocity!!!!
Thnx
Hang on, diagram is wrong! Whoops. Hold on a sec and I'll do it again.

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