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OCR Advancing Physics G492 ~5 June 2013~

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With the trolley on the ramp, it has an acceleration, g, acting directly downwards. If we take the component of this force parallel to the plane (using the cos rule, as it's an enC(os)losed angle), we get a=(9.81)(sin(theta)) => a=g.sinϴ

If we then substitute this into the equation v²=u²+2as with u=0, we get that result (v² =2.g.l.sinϴ). Also it's probably worth noting that plotting a graph with v^2 against sinϴ gets us with a gradient of 2.g.l

Thank you so much!! It's frustrating that there are so many mathsy questions which I suck at :cool:

Reply 141

seharnaznaz

Original post by marseille_h

Antinodes is where the intestity is the highest compared to nodes where it is =0

Thank you!

Reply 142

vithusan40

The opening questions of the physics paper is normally units.....(E.g 1J=1Nm)
Can someone post as many of these types of equations and units that can come up??

Reply 143

Oliver_H

Timing recommendations for each section?

Reply 144

gary96

Original post by oliver_h

timing recommendations for each section?

a 20
b 40
c 60

Reply 145

Iamtidal

Original post by gary96

a 20
b 40
c 60

b and c are the same amount of marks, so i like to do 40 40 and leave 20 mins for checking.

Reply 146

ArchieL

Original post by vithusan40

The opening questions of the physics paper is normally units.....(E.g 1J=1Nm)
Can someone post as many of these types of equations and units that can come up??

Just think equations!
Force (N) = ma = kgms^-2
Work (J) = Fd (Nm, Kgm^2s^-2)
Power (J/s) = Fv = Js^-1 = Nms^-1

etc etc

Reply 147

reebop

Original post by Mathletic

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!

Really great post. You say that the size of the card caused problems in the result, why do you think a larger card created bigger errors? Was it because the trolley had accelerated a little more by the time it cleared the light beam, or do you think its something else.

Reply 148

vithusan40

With the Pre-Release material, what are the key points we should prepare for before the exam?

Reply 149

Mathletic

Well the light gateworks by sensing a sudden change in light, if you imagine moving a pencil through a light gate fairly slowly you could get a reading of say half 0.1 ms-1, the light gate noticed that something passed and covered the sensors on the light gate, so you may get a reading of say 0.13 ms-1

Now if you moved a piece of card which is much longer than the penceil (width) and if you moved that past the light gate at 0.1ms-1 as well... both objects are ACTUALLY moving at 0.1ms-1 but because of the added length to the card the sensor is covered up longer,

The lightgate now thinks Ahh this is a slow object because the sensors have been covered up longer! Does that make sense its hard to describe,

Similarly if you moved a piece of wood thats a meter long through the lightgate at 10ms-1 the sensors would be coverd up the same amount of time as a block moving past very slow, they will both give the same reading on the light gate but there ACTUAL speeds are different

It all whittles down to speed distance time, we had a data logger which required you to enter the width of the object passing through it to avoid this error, (ie calibrating it)

SORRY MEANT TO QUOTE THIS TO REEBOP

(edited 10 years ago)

Reply 150

ArchieL

Well it's bed time now.. See you on the other side folks.

Reply 151

ArchieL

Original post by vithusan40

With the Pre-Release material, what are the key points we should prepare for before the exam?

Have a look at my earlier post with links to prerelease questions, it may help :smile:

Reply 152

Mathletic

Original post by ArchieL

Well it's bed time now.. See you on the other side folks.

Best of luck and thanks for the pre release material!

Reply 153

Mathletic

Original post by reebop

sorry i replied but forgot to quote its somewhere on this page i think :P

Reply 154

marseille_h

https://www.khanacademy.org/science/physics/forces-newtons-laws/inclined-planes-friction/v/inclined-plane-force-components

might be usefull

Reply 155

Mathletic

Everyone check graph units before calculating gradients etc especially on section c :smile:

good luck all !!!

Reply 156

sarjan100

Original post by Tejmasta

Anyone else think the section c questions are not really physics?

Not really it's applied. G491 was a bunch of non physics, not section c of G492 with "estimate the number of pages in an ebook", and " how many beats per minute does this ecg show". etc