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

1. -are heat engines and laws of thermodynamics in our syllabus?? its there in the old syllabus books

and what about specific latent heat of vaporisation and fusion??

and gravitational potential ?

EDIT: sorry for triple posting
2. (Original post by kosy91)
-are heat engines and laws of thermodynamics in our syllabus?? its there in the old syllabus books

EDIT: sorry for triple posting
Thermo
1. Energy not created or destroyed.
2. Entropy increases.
3. Can't obtain absolute 0

Don't think you need to specifically know them, though.
3. The gravitational field strength on the surface of the Earth is g. The gravitational field
strength on the surface of a planet of twice the radius and the same density is
A 4 g
B 2 g
C g
D g/ 4

how do you solve these types of questions?
4. This paper better not be like Unit 4, i felt prepared for unit 4 and that paper a nightmare!!
Not sure im fully ready now :P
5. (Original post by jellyman330)
This paper better not be like Unit 4, i felt prepared for unit 4 and that paper a nightmare!!
Not sure im fully ready now :P
Probably will be mad. Edexcel don't like us this year
6. (Original post by fredbraty)
awww many many thanks!That's what i thought too.
Best of luck tomorrow my friend!
you too!

I think this paper has the potential to be terrible, if the biologists in my year are representative of the world... encouraging.

Look on the bright side: bad paper = lower boundaries = easier to get an A (if you know your stuff)
7. (Original post by Joann79)
The gravitational field strength on the surface of the Earth is g. The gravitational field
strength on the surface of a planet of twice the radius and the same density is
A 4 g
B 2 g
C g
D g/ 4

how do you solve these types of questions?
g=(G*rho* 4/3* piR^3) over R^2
so G=(3g)/(4pi*R*rho)

let gravitational potential strength at other planet be x

so x=(G*rho* 4/3* pi(2R)^3) over (2R)^2

put it the value of G from above

8. Damping reduces the resonant frequency, the natural frequency never changes.
9. (Original post by Kameo)
Damping reduces the resonant frequency, the natural frequency never changes.
yes thats true
when a system has been damped, the frequency at which resonance occurs is lower than the natural frequency. the frequency at which this phenomenon occurs is known as resonant frequency
10. (Original post by Joann79)
The gravitational field strength on the surface of the Earth is g. The gravitational field
strength on the surface of a planet of twice the radius and the same density is
A 4 g
B 2 g
C g
D g/ 4

how do you solve these types of questions?
This is the way I do it, it's probably longer than others

This is for earth

We know that density is mass over volume

So mass

Assuming it's spherical, V is equal to

Replace the V in M=pv with that^ and then place M into the gravitational field strength equation.

So

The r squared and r cubed cancel leaving you with

It's got twice the radius and same density. So for this new planet r = 2r

Edit: Haha Kosy's method is MUCH less work, both work fine though.
11. (Original post by Sasukekun)
This is the way I do it, it's probably longer than others

This is for earth

We know that density is mass over volume

So mass

Assuming it's spherical, V is equal to

Replace the V in M=pv with that^ and then place M into the gravitational field strength equation.

So

The r squared and r cubed cancel leaving you with

It's got twice the radius and same density. So for this new planet r = 2r

Edit: Haha Kosy's method is MUCH less work, both work fine though.

doesnt matter as long as you get the right answer. hows revision going?
12. OOOOOOOOOOOOOOOOOOOOoooooooooooo oooooooooo <24 hours to go

Im jus happy this is my last exam, , after chem5 this morning.
Although i dnt do biology its quite annoying that all three sciences are so crammed together. Wish they were more evenly spaced out...

nywayz need to strt revision
howz every1 finding this unit??? I think its of the easier units, learning wise, tht we hv had so far
(myte b bcoz i did m3 n m4 so helpd a lot with oscilations )
13. (Original post by Sasukekun)
This is the way I do it, it's probably longer than others

This is for earth

We know that density is mass over volume

So mass

Assuming it's spherical, V is equal to

Replace the V in M=pv with that^ and then place M into the gravitational field strength equation.

So

The r squared and r cubed cancel leaving you with

It's got twice the radius and same density. So for this new planet r = 2r

Edit: Haha Kosy's method is MUCH less work, both work fine though.
For those type of questions I like to see what g is proportional to in context of the question, this avoids writing down, unecessary figures such as 4, pi, m, p etc.

In this case g is proportional to 2^3/2^2 so the scale factor is 2
14. (Original post by Kameo)
For those type of questions I like to see what g is proportional to in context of the question, this avoids writing down, unecessary figures such as 4, pi, m, p etc.

In this case g is proportional to 2^3/2^2 so the scale factor is 2
BRAVO!!!!!!!!!

now thats the best answer i have seen in quite some time
15. anyone know if heat engines are in the syllabus??
16. I've got a few questions.

- How do you deduce the colour of a star from its power/wavelength spectrum?
- In nuclear fissions and nuclear fusion would it be better to say that a change in mass releases energy according to ΔE = c²Δm, or would it be equally correct to say that the total binding energy per nucleon is greater than that before?
- How exactly can a Doppler shift from a star be found, is it just to transmit a pulse of electromagnetic radiation to the star and see what wavelength comes back, and using the redshift formula to work out its velocity? Is there a specific view of the star that must be considered in order for this to happen (i.e. we must be seeing it horizontally perpendicular to the line between the star and any planets so that the star appears to either wobble towards or away from us, if that makes sense?)
17. Don't they get the absorption spectrum from the light emitted from the star, so yes it would be electromagetic emission.
18. (Original post by OL1V3R)
I've got a few questions.

- How do you deduce the colour of a star from its power/wavelength spectrum?
If all the colours in the spectrum are blue-leaning, you know it's blue. etc.
Also, the more power emitted from the star, the bluer it is. <Although this also has to do with size. [hence, blue supergiants and red dwarfs]

- In nuclear fissions and nuclear fusion would it be better to say that a change in mass releases energy according to ΔE = c²Δm, or would it be equally correct to say that the total binding energy per nucleon is greater than that before?

- How exactly can a Doppler shift from a star be found, is it just to transmit a pulse of electromagnetic radiation to the star and see what wavelength comes back, and using the redshift formula to work out its velocity? Is there a specific view of the star that must be considered in order for this to happen (i.e. we must be seeing it horizontally perpendicular to the line between the star and any planets so that the star appears to either wobble towards or away from us, if that makes sense?)

[i]They use the absorption spectrum, and then compare it to a lab sample on Earth.
Nothing else is needed...
hope that clears it up!
19. (Original post by kosy91)
yes thats true
when a system has been damped, the frequency at which resonance occurs is lower than the natural frequency. the frequency at which this phenomenon occurs is known as resonant frequency
why doesnt it increase the resonant frequency? surley a damped system should require more energy?
20. (Original post by kosy91)
anyone know if heat engines are in the syllabus??
I don't think so! I've not seen them in the Miles Hudson book, and I just looked through the specification - it's not there!

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