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

1. (Original post by fredbraty)
yess they wanted maximum,but the formula they gave us was for the maximum speed.also, the points were few so it shouldnt require any other work.
How did you find the K.E that high?
yess you should divide by 71.dont worry though you wont lose a lot.
Really? but why did they want the uncertainties in the previous parts?
2. (Original post by Joann79)
Really? but why did they want the uncertainties in the previous parts?
for the very last question where you should find the percentage uncertainty for the kinetic energy.
3. (Original post by fredbraty)
for the very last question where you should find the percentage uncertainty for the kinetic energy.
I guess i really messed that question up

How much do you think id lose marks?
4. (Original post by fredbraty)
for the very last question where you should find the percentage uncertainty for the kinetic energy.
5. Got v =0.58ms^-1, E=0.16J.

Didnt have any problems with the scale.. Used scales of 2 and 5.
6. (Original post by Joann79)
dont worry.There's always upgrade in physics exams.Also unit 6 doesnt affect the overall grade much.

Sure i will write what i remember.
well i think at first i asked the uncertainty of height which is the uncertainty of the ruler,i.e the smallest division,1mm.
Then it asked for the uncertainty of the time.I did the half range value.i.e (max-min)/2 and it was >0.5 so i accepted it.
Then it asked for the max mean square speed.I used the formula and on the denominator i used the mean value for time which was 3.03 as i can remember.The speed i got was 0.58 but i didnt add any uncertainties.I sont think we should but i might be wrong.
Then for the kinetic energy,it said the total kinetic energy,so i added the kinetic energy of mass1 + K.E of mass 2.I did not do 0.5x(m+M)xu^2 since the two bodies are not attached to each other.
For the last part,the percentage uncertainty of K.E=4x %unertainty of u.And percentage uncertainty of u=%uncertainty of h + % uncertainty of t.I got something like 4%?But i am not sure,it might be from another question.
Oh!And the kinetic energy i found it to be 0.16J.

Hope it helped.
Got v =0.58ms^-1, E=0.16J.

Didnt have any problems with the scale.. Used scales of 2 and 5.
same here yadas.but i used a scale of 2.5 so that the graph would be bigger.
8. (Original post by fredbraty)
dont worry.There's always upgrade in physics exams.Also unit 6 doesnt affect the overall grade much.

Sure i will write what i remember.
well i think at first i asked the uncertainty of height which is the uncertainty of the ruler,i.e the smallest division,1mm.
Then it asked for the uncertainty of the time.I did the half range value.i.e (max-min)/2 and it was >0.5 so i accepted it.
Then it asked for the max mean square speed.I used the formula and on the denominator i used the mean value for time which was 3.03 as i can remember.The speed i got was 0.58 but i didnt add any uncertainties.I sont think we should but i might be wrong.
Then for the kinetic energy,it said the total kinetic energy,so i added the kinetic energy of mass1 + K.E of mass 2.I did not do 0.5x(m+M)xu^2 since the two bodies are not attached to each other.
For the last part,the percentage uncertainty of K.E=4x %unertainty of u.And percentage uncertainty of u=%uncertainty of h + % uncertainty of t.I got something like 4%?But i am not sure,it might be from another question.
Oh!And the kinetic energy i found it to be 0.16J.

Hope it helped.
Thank youuu so much it really helpedd!! i really hope is an eco or somthing for the speed if i got it wrongg

Oh well as you said it doesnt affect. Thanks again
9. What did everyone get for the percentage error in KE?

To find the error in velocity, I did percentage error in time plus percentage error in height. Then I multiplied that by two to find percentage error in KE. Would that be right? Gave me around 17%, which doesnt seem to be what other people got..
10. (Original post by dancing.barefoot)
What did everyone get for the percentage error in KE?

To find the error in velocity, I did percentage error in time plus percentage error in height. Then I multiplied that by two to find percentage error in KE. Would that be right? Gave me around 17%, which doesnt seem to be what other people got..
K.E=0.5*m1*v^2+0.5*m2*v^2
so the %uncertainty of K.E=4*%uncertainty of u.
yess for %uncertainty of u=%uncertainty of h + %uncertainty of t
how did you find the K.E?Did you do 0.5*(m+M)*v^2?or 0.5*m1*v^2+0.5*m2*v^2 ?
maybe that's why you found it differently.
11. (Original post by Joann79)
Thank youuu so much it really helpedd!! i really hope is an eco or somthing for the speed if i got it wrongg

Oh well as you said it doesnt affect. Thanks again
sure
12. how do you use the two columns in the radioactivity question?
13. (Original post by fredbraty)
(Original post by wooper)
If velocity is less than 1 m/s, then kinetic energy should be less than 1J (mass was about 1 kg?). But using GPE and conservation of energy, we get mgh = 1 kg*10 m/s^2*1 m approximately, which is 10 J. What is going wrong here? Maybe we used the wrong units somewhere, e.g. mm instead of m?
the masses were in grams..the height was in mm,so reasonable
Can you remember what the masses were? Were they 0.930 kg and 0.030 kg? The height was 885 mm. I can't remember which mass was dropping. If it was the lighter one, using mgh gives energy = 0.03 * 9.81 * 0.885 = 0.26 J. If it was the heavier one, mgh = 0.93 * 9.81 * 0.885 = 8.07 J.

I got 0.584 m/s for the velocity, giving energy = 0.5 *(0.93+0.03)* (0.584)^2 = 0.16 J.

Where is the energy going?

There cannot be friction or air resistance, because using s=0.5(u+v)t where u = 0, gives v = 2s/t , i.e. 2h/t, which is the formula given.
14. (Original post by dancing.barefoot)
What did everyone get for the percentage error in KE?

To find the error in velocity, I did percentage error in time plus percentage error in height. Then I multiplied that by two to find percentage error in KE. Would that be right? Gave me around 17%, which doesnt seem to be what other people got..
I did that too, but got 20%, probably because I took the uncertainty in the time to be 0.3 and you did 0.26?

In the percentage uncertainty of the diameter, I used half the range (0.02mm) rather than the precision of the micrometer (0.01mm) and got 7%. Anyone else?

And in the last questions I got around 0.05mm^-1 for mu, but were we not supposed to include units, since it asked for the value?
15. (Original post by wooper)
Can you remember what the masses were? Were they 0.930 kg and 0.030 kg?
exactly
16. (Original post by AyonFazal)
how do you use the two columns in the radioactivity question?
you subtract the background radiation to calculate A
and the other column you do ln(A/minute^-1)
17. (Original post by AyonFazal)
how do you use the two columns in the radioactivity question?
One would be the corrected Activity, A (i.e. Recorded Count - Background count), and the other would be ln A.

Silly me only realised the background count value when I had a minute left didn't have time to correct my graph

(Original post by Xtian)
And in the last questions I got around 0.05mm^-1 for mu, but were we not supposed to include units, since it asked for the value?
I doubt they are fussy about that
18. (Original post by Xtian)
I did that too, but got 20%, probably because I took the uncertainty in the time to be 0.3 and you did 0.26?

In the percentage uncertainty of the diameter, I used half the range (0.02mm) rather than the precision of the micrometer (0.01mm) and got 7%. Anyone else?

And in the last questions I got around 0.05mm^-1 for mu, but were we not supposed to include units, since it asked for the value?
the unertainty in time is the half range value wich comes out to be >0.5 s,i think.
yess i got about 7% i think.
yess it was 0.0506666
19. (Original post by fredbraty)
the unertainty in time is the half range value wich comes out to be >0.5 s,i think.
yess i got about 7% i think.
yess it was 0.0506666
Hmmm are you sure it was >0.5? I think the range was 0.52, and half of that is 0.26.
20. (Original post by dancing.barefoot)
What did everyone get for the percentage error in KE?

To find the error in velocity, I did percentage error in time plus percentage error in height. Then I multiplied that by two to find percentage error in KE. Would that be right? Gave me around 17%, which doesnt seem to be what other people got..

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