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Author Topic: Physics P5 questions  (Read 3008 times)

Offline Gaz

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Physics P5 questions
« on: June 08, 2010, 04:49:14 pm »
Usually the 2nd question requires drawing a graph with a line of best and worst fit. Is the error in the gradient of the line of best fit calculated by (gradient of best-fit line – gradient of worst acceptable line)?
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Offline falafail

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Re: Physics P5 questions
« Reply #1 on: June 08, 2010, 04:53:17 pm »
yep.
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Offline falafail

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Re: Physics P5 questions
« Reply #2 on: June 08, 2010, 04:55:48 pm »
quick question:
which of these is considered the line of best fit?

this
http://i45.tinypic.com/29ys9c3.png
or this
http://i46.tinypic.com/k0od9d.png
??
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Offline Gaz

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Re: Physics P5 questions
« Reply #3 on: June 08, 2010, 04:57:23 pm »
Quote from: falafail on June 08, 2010, 04:55:48 pm
quick question:
which of these is considered the line of best fit?

this
http://i45.tinypic.com/29ys9c3.png
or this
http://i46.tinypic.com/k0od9d.png
??

i believe it is the 2nd one:
http://i46.tinypic.com/k0od9d.png
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Offline falafail

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Re: Physics P5 questions
« Reply #4 on: June 08, 2010, 04:58:43 pm »
Quote from: Gaz on June 08, 2010, 04:57:23 pm
i believe it is the 2nd one:
http://i46.tinypic.com/k0od9d.png

i know it LOOKS right but the first one passes through more points  :-\
and what exactly IS the line of best fit? isn't it the line that passes through the most points?
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Offline Gaz

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Re: Physics P5 questions
« Reply #5 on: June 08, 2010, 05:10:21 pm »
Yup. I too am not sure of the definition of a line of best fit. Use this:
http://staff.argyll.epsb.ca/jreed/math9/strand4/scatterPlot.htm
It might help in understanding the line of best fit.
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Offline Onion

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Re: Physics P5 questions
« Reply #6 on: June 08, 2010, 05:20:08 pm »
True. Your first passes through more points but that's not the line of best fit for sure as 2 points are above the lines =)

For a line to be a best fit - it must passes through most points (though not necessarily) or most points must lie evenly along the line. For e.g. you can't have 2 points above the line (as in your first line) and none below. If 3 points are above the line, there should also be 3 points below - hence, evenly spread.

Hope it make sense =]
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Offline Gaz

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Re: Physics P5 questions
« Reply #7 on: June 08, 2010, 05:22:12 pm »
I just checked. Your right. There has to be just as many points above the line as below. One either way if the number of points are odd.
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Offline falafail

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Re: Physics P5 questions
« Reply #8 on: June 08, 2010, 05:31:02 pm »
hmm alright, thanks
i have another question.. in nov 09 the second variant, question 2 part d
to calculate the uncertainty i multiplied the percentage error in the gradient by the value i got for g, and i got 1.5
in the mark scheme it says to subtract the g you get from the gradient - g from worst acceptable line.. if i do that, i get 1.2

is my way also correct?
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Offline wildrider

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Re: Physics P5 questions
« Reply #9 on: June 08, 2010, 05:34:47 pm »
Quote from: falafail on June 08, 2010, 04:55:48 pm
quick question:
which of these is considered the line of best fit?

this
http://i45.tinypic.com/29ys9c3.png
or this
http://i46.tinypic.com/k0od9d.png
??

the 2nd one is the line of best fit
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Offline Twinkle Charms

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Re: Physics P5 questions
« Reply #10 on: June 08, 2010, 06:33:05 pm »
one more question ,
How do we calculate absolute errors in the values of l^2??

the paper is attached, Q2 (b)
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Offline falafail

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Re: Physics P5 questions
« Reply #11 on: June 08, 2010, 06:34:44 pm »
Quote from: Zara on June 08, 2010, 06:33:05 pm
one more question ,
How do we calculate absolute errors in the values of l^2??

the paper is attached, Q2 (b)

percentage error in l^2 = percentage error in l X 2
multiply that by whatever value you get for l^2
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Offline falafail

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Re: Physics P5 questions
« Reply #12 on: June 08, 2010, 06:36:13 pm »
Quote from: falafail on June 08, 2010, 05:31:02 pm
in nov 09 the second variant, question 2 part d
to calculate the uncertainty i multiplied the percentage error in the gradient by the value i got for g, and i got 1.5
in the mark scheme it says to subtract the g you get from the gradient - g from worst acceptable line.. if i do that, i get 1.2
is my way also correct?

anyone? :(
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Offline iq101

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Re: Physics P5 questions
« Reply #13 on: June 08, 2010, 07:00:31 pm »
Quote from: falafail on June 08, 2010, 06:36:13 pm
anyone? :(

Hmm. But personally i think the whole point of drawing a worst acceptable line is to calculate errors so yeah. Stick to the mark scheme method.
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Offline princesszahra

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Re: Physics P5 questions
« Reply #14 on: June 08, 2010, 07:43:40 pm »
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