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# 19/05/10 Edexcel Phy 6(6PH08) watch

1. (Original post by dancing.barefoot)
When you're finding the percentage uncertainty of two quantities added together, it isn't as simple as just adding each individual percentage uncertainty.. From what I understand anyway - but I suck at this stuff.

And surely, if both methods were correct, they would give the same percentage uncertainty..

Absolute uncertainty is, for example, 0.26 for reaction time.
true but both are logical...
if you have a sum,multiplication,division,subt raction then you add the uncertainties....
ehmm anyway we will see in August...
Good luck!
2. (Original post by fredbraty)
true but both are logical...
if you have a sum,multiplication,division,subt raction then you add the uncertainties....
ehmm anyway we will see in August...
Good luck!
Yes but you add absolute uncertainties when you have a sum or subtraction.. You add percentage uncertainties when you have multiplication or division.

Oh well, we'll see when the mark scheme comes out.

Good luck to you as well
3. (Original post by fredbraty)
wooper the height was 685 mm.i am sure
so no energy lost
so confirms the formula they gave us
I remember it as 885 mm, and have still got 885 on my calculator.

But even if it was 685 mm, there is still a big discrepancy between energy = mgh and energy = 0.5*(M+m)*v^2.

Can you remember whether it was the light or heavy mass that falls?

Using either 0.93 kg or 0.03 kg with mgh gives a different figure for lost GPE than for gained KE using 0.93+0.03 as the mass, whether the height was 885 mm or 685 mm
4. (Original post by wooper)
I remember it as 885 mm, and have still got 885 on my calculator.

But even if it was 685 mm, there is still a big discrepancy between energy = mgh and energy = 0.5*(M+m)*v^2.

Can you remember whether it was the light or heavy mass that falls?

Using either 0.93 kg or 0.03 kg with mgh gives a different figure for lost GPE than for gained KE using 0.93+0.03 as the mass, whether the height was 885 mm or 685 mm
lol wooper,first relax.you will get a heart attack lol
it should have been the heavier one or else it wouldnt fall.
Then there could be friction or other forces acting.
If it was 685 mm then the g.p.e lost >k.e gained which means there was loss of energy,probably due to friction.
5. (Original post by fredbraty)
lol wooper,first relax.you will get a heart attack lol

it should have been the heavier one or else it wouldnt fall.
It would fall if there was no friction.
Then there could be friction or other forces acting.
If it was 685 mm then the g.p.e lost >k.e gained which means there was loss of energy,probably due to friction.
Point taken. v=2h/t implies constant acceleration, but the model could assume a constant frictional or other retarding force. (885 mm gives GPE lost > KE gained too).

Does anyone else remember the height as 685 mm?
885 mm tallies with the 0.16 J figure people got. 685 mm gives 0.098 J.
6. (Original post by wooper)

It would fall if there was no friction.

Point taken. v=2h/t implies constant acceleration, but the model could assume a constant frictional or other retarding force. (885 mm gives GPE lost > KE gained too).

Does anyone else remember the height as 685 mm?
885 mm tallies with the 0.16 J figure people got. 685 mm gives 0.098 J.

Also it was the apparatus of an experiment,and the question had a bench not an air track where we could assume no friction.
7. (Original post by fredbraty)

Also it was the apparatus of an experiment,and the question had a bench not an air track where we could assume no friction.
OK OK you're right! So that's where the energy went

Just hoping it was 885 mm.
8. (Original post by wooper)
OK OK you're right! So that's where the energy went

Just hoping it was 885 mm.

maybe it was,what's for sure is that u=0.58 m/s and K.E=0.16J
Are you going to do unit 5 and unit 4 this June also?
9. guys....for sure it was 885mm!!
10. (Original post by Doughboy)
OH MY GOD GUYS.

Did they really give us BG count rate in Q4?

I swear I didn't read that so I just found ln A and used one column. Hopefully I'm only penalised once for it though. I just need a B in this paper.
Hehe, me too.
Didnt find the BG count-rate.. though I mentioned it in the experiment description.
11. (Original post by fredbraty)
Are you going to do unit 5 and unit 4 this June also?
Only unit 5; I did unit 4 in Jan. Are you doing both in June?
12. It was 885 mm!
13. (Original post by wooper)
Only unit 5; I did unit 4 in Jan. Are you doing both in June?

good luck wooper!
14. (Original post by dancing.barefoot)
Yes but you add absolute uncertainties when you have a sum or subtraction.. You add percentage uncertainties when you have multiplication or division.

Oh well, we'll see when the mark scheme comes out.

Good luck to you as well
P.S:You cant do any calculations with absolute uncertainties.For example if u=2h/t
you are not allowed to find the absolute uncertainty of h and then add it to the absolute uncertainty of t because they are two completely different physical quantities.The absolute uncertainty of h is in mm and the absolute unertainty of t is in seconds.You cant add 1mm+0.26s and say that the unertainty of u is 1.26.
This is only allowed in % uncertainties because they are all percentages.
15. Do you remember how many marks were on the K.E. question in total?
16. (Original post by Joann79)
Do you remember how many marks were on the K.E. question in total?
Q1 - measurement - wire - 7 marks (1,1,1,1,1,2)
Q2 - mechanics - trolley and weight - 10 marks
Q3 - cosmology - Hubble's constant - 6 marks (1,1,2,1,1)
Q4 - nuclear decay - gamma rays - 17 marks (3,6,1,5,2)

What did people get for μ in Q4? I got 0.0505 mm^-1
17. (Original post by fredbraty)
good luck wooper!
Good luck to you too
18. (Original post by kosy91)
i got the same and so did many of my classmates!!!

I think i'm up for a 60 again
19. (Original post by wooper)
What did people get for μ in Q4? I got 0.0505 mm^-1
I got around 0.05 too.
20. (Original post by wooper)
Q1 - measurement - wire - 7 marks (1,1,1,1,1,2)
Q2 - mechanics - trolley and weight - 10 marks
Q3 - cosmology - Hubble's constant - 6 marks (1,1,2,1,1)
Q4 - nuclear decay - gamma rays - 17 marks (3,6,1,5,2)

What did people get for μ in Q4? I got 0.0505 mm^-1
0.050566666

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