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OCR Advancing Physics G492 ~5 June 2013~

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Reply 40

Europa192

And does anyone have ideas for systematic errors for the trolley experiment. I was thinking: - Measurement of the card - length of ramp, measuring the ramp from the back of the trolley from the starting end to the front of the trolley at the end of the ramp - mass of trolley. Anymore ideas?

Reply 41

AmethfulEm

Original post by Europa192

Does anyone have a link to the mark scheme for Jan 2013?

Here you go, I'm pretty sure that's the right one anyway.

Does anyone think that it'll ask for an alternative way of conducting the experiment, e.g. altering of variables or such? I hadn't thought of this before, but hey you never know what could come up.

Reply 42

King Hotpie

Original post by AmethfulEm

For my coursework I used the rather cruder method of dropping a weight and card straight through a light gate to measure g. Do you reckon that will do?

Reply 43

Mathletic

Original post by Europa192

I actually did this experiment for my coursework!! however I decided to prove the relationship between acceleration and displacement but I used exactly the same set up!
Your absolutely right with the length of the card, this influences the data hugely, especially at lower speeds where the trolley passes the light gate the card just distorts the data - it prevents the true speed to be detected.
To reduce this systematic error you can shorten the length of card but if its too thin the light gate wont detect it!!!

The friction on the ramp also influences the speed the trolley travels down the ramp, of course you want to reduce resistance so reduce surface area of wheels and use a smoother ramp perhaps?

As for the angle this was the hardest part to get right in my experiment, primarily due to paralax errors distorting the true angle, I used a larger protractor to get my angle so i could align the ramp and the radii of the protractor, this is more accurate than using a small protractor, I also experimented using trigonometry because you know all the lengths! this was very boring and time consuming so I just used protractor in the end!

Im also thinking the light gate must be calibrated properly to avoid zero errors? They may get us to plot a graph based on v^2 = u^2 +2as?

Oooh and one last thing, ensuring the trolley goes STRAIGHT down the ramp! Probably wont be asked but mine had a wonkey axel so I had to mend it!

Reply 44

Europa192

Original post by Mathletic

Thank you! That's a big help, I always get stuck on questions about improving experiments. You must have been over the moon when you saw this experiment on the pre release :smile:

Reply 45

Europa192

Original post by AmethfulEm

Thanks for the link. :smile:

And I was thinking they might want us to suggest an experiment for measuring the resistive force of the ramp? My idea would be to find the angle the ramp needs to be at to let the trolley roll without getting faster or slower.

Reply 46

zcQ

What two variables would you plot for the trolley experiment to find g?
Thanks

Reply 47

BigBear7

Hi, does anyone have any good revision material for section C? I'm resitting it outside of school, but when I first did it my school provided me this revision sheet with definitions of sensitivity and resolution etc.?

Thanks

Reply 48

marseille_h

Hi, anyone got the question paper for january 2013 ?

Thanks :smile:

Reply 49

Mabes

Original post by marseille_h

Hi, anyone got the question paper for january 2013 ?

Thanks :smile:

Both the paper and the mark scheme are already linked on this thread.

Reply 50

_Lydia_

When doing the mathy questions- to what sig figs do they want the answer if they don't specify it? Do you still get all marks if you put more sig figs than the answer on the mark scheme? :erm:

Reply 51

King Hotpie

Original post by _Lydia_

When doing the mathy questions- to what sig figs do they want the answer if they don't specify it? Do you still get all marks if you put more sig figs than the answer on the mark scheme? :erm:

This. I always put 3 out of habit (unless doing things like uncertainties), but the mark scheme normally has 2. I really don't want to have to change it, I'm way too OCD about not giving specific answers. Can anyone shine some light onto the matter?

Reply 52

jelmes96

Original post by Paribas01

What two variables would you plot for the trolley experiment to find g?
Thanks

if a = gSinPHETA
Then given a value for a, and you know the angle, g = a/ SinPHETA. If you plot acceleration over SinPHETA, then the gradient should be 9.8ms^-2.

Also, Another factor which you could encounter with difficulty, is the value for Pheta. Trying to measure the angle of a ramp is incredibly difficult with a protractor. So what me and my friend did (Jaetpa), was we measured the length of the ramp, and the height of the ramp, because finding the length (parallel to the horizontal plane), is incredibly difficult, and you will encounter parallex. Therefore, measuring h and L, you can use basic trig, to find out PHETA. This of course would be: PHETA = ArcSin (height / length) = Sin^-1(opposite/hypotenuse).

The thing is, you don't need m, and you don't need fr etc, unless they wanted you to resolve the forces. (Good if you do M1 in maths.) That would be you resolve forces parallel and perpindicular to the plane. then, parallel to the plane, acceleration = (Forces in direction of motion - Forces opposing the direction of motion) / mass of the trolley

Good luck everyone :biggrin:

(edited 10 years ago)

Reply 53

jelmes96

Original post by _Lydia_

When doing the mathy questions- to what sig figs do they want the answer if they don't specify it? Do you still get all marks if you put more sig figs than the answer on the mark scheme? :erm:

Normally 3 significant figures, unless the figures you're given are 1 or 2 significant figures. But generally, go with 3 significant figures. You can only be penalised once durinng the exam for inappropiate significant figures.

Reply 54

SherlockHolmes

Original post by _Lydia_

When doing the mathy questions- to what sig figs do they want the answer if they don't specify it? Do you still get all marks if you put more sig figs than the answer on the mark scheme? :erm:

Original post by King Hotpie

You should give 3 significant figures for all calculations excepted when asked for a percentage. If you are asked to calculate a percentage then give to 2 decimal places.

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Reply 55

Chris_Shaw1

for those who are interested

(edited 10 years ago)

Reply 56

King Hotpie

Original post by Chris_Shaw1

for those who are interested

What does the third one with all the AOs mean? :s-smilie:

Reply 57

RATKING

How long does everyone spend on each section?

Reply 58

Iamtidal

Original post by RATKING

How long does everyone spend on each section?

Normally section A only takes 20 mins max and I find section C shorter than B, maybe 30-40 mins on each with time to check.

Reply 59

RATKING

Original post by Iamtidal

Normally section A only takes 20 mins max and I find section C shorter than B, maybe 30-40 mins on each with time to check.

Thanks, I normally spend 20 mins on A and 40 on B. But I haven't been doing section C's because then I have to waste time reading their pre-releases and its quite irrelevant. But I've done some section C's at school, just not timed, as well questions people have put together for our section C article.