*** Leaving Cert PHYSICS 2014 ***

Days 298

That was a lovely paper. Particles physics question was different. A2 at least in the bag .

Solid_Shepard

LCMATHS wrote: »

I was going to say air resistance, but isn't air resistance just a type of friction?

While I believe it is indeed a frictional force as you've said, it is different from the friction that would occur between the table and the trolley in that the drag is dependant upon the object's velocity (amongst other factors such as the cross sectional area). It's really dependant upon the marking scheme as to whether or not they would accept both friction and it as two seperate points (I'd be doubtful, but not completely unwilling to entertain the possibility).

EDIT: Regarding it being weight or gravity, the force diagram of a single trolley can be seen here if the runway were to be placed at an angle. i.imgur.com/dgqmndy.png. In this instance, it's the component of weight parallel to the track that's going to be dragging it down (as the force is mgSina, where a is the angle between the runway and level ground). However, because the weight is due to the fundamental force of gravity, that, too, can be considered valid. Ultimately, however, it really doesn't make much of a difference; there is no way they'll nitpick that harshly. If they did, there would be complaints in all parts of the country.

AtomicKoala

Ok, now that everyone has said the paper was easy, did anyone else think it was actually quite.. difficult?

Peregrine

AtomicKoala wrote: »

Ok, now that everyone has said the paper was easy, did anyone else think it was actually quite.. difficult?

I thought Q5 was the most difficult I've ever seen.
The last part of Q6, the mechanics question, would've been very difficult for the non-Applied Maths folk. Other than that, the ones I did were fairly decent. Not easy but decent.


I had planned on completely skipping electricity (except Joule's Law, I expected that to come up) and when I saw Q10, it broke my heart. Such an easy Doppler effect question..with electricty Ended up doing it and ****ing up the whole Wheatsone bridge part.

EoghanIRL

AtomicKoala wrote: »

Ok, now that everyone has said the paper was easy, did anyone else think it was actually quite.. difficult?

There was no gruellingly difficult calculations.
Theory was easier than usual .
No curveball this year in section A .
It was much easier than past papers . It was only easy if you knew your stuff I guess .


Anyone think there was more derivations than usual ?

FatRat

Q5 was definitely the hardest I've seen yet. Section A was no walk in the park either really. The last part in q1 and q3 could've thrown people off. The option question, I thought, was one of the hardest option questions yet. I was certain on doing that Q but ended up opting to skip it! Says a lot....


Apart from that I thought it was much easier than normal, especially for those who studied electricity a lot. Q9 and Q10 were very easy. I think those who were relying on q5 and the option question for two of their long questions were hit hard though.

qweerty

That I can see, the only way to do the last part of Q6 is to calculate th vertical component of the velocity, and then to use either equations of motion or KE=PE to get max height.

@Nimrod7 I was only joking in saying the examiner would think him a prat for showing off (obv!), but it was unnecessary to get TMH and all that jazz. I would say the same of someone else's approach, which involved differentiating a function when we already have an equation for the first integral.

I think it's a pretty standard paper without too many surprises. But an unprepared student would struggle, IMO.

FatRat

I didn't even do the mechanics question but I always though that to get max height all you need to do was find the height when the velocity = 0 ?

Solid_Shepard

AtomicKoala wrote: »

Ok, now that everyone has said the paper was easy, did anyone else think it was actually quite.. difficult?

I thought some parts were, while others were fine. There were some odd questions featured, some potentially unclear elements, and a lot of mixing of topics in questions.

Question one was fine. Asking for two forces rather than just one could have been a slight issue for some, but overall this was a fairly standard momentum in collisions experiment question.

Question two was fine, but the last part was very unusual; it seems possible to just waffle an answer if you're stuck however.

Question three was standard, except for that absolutely bizarre final part (which I certainly got wrong), where it was asking you to talk about graphing/getting the slope (as the y-intercept = -.03d) without actually asking about it directly that.

Question five was more difficult than usual I felt; the U-value question is not common, the pair of complimentary colours was unusual (not particularly difficult, but odd), Rutherford's model could be confused for the 'plum-pudding', and depending upon your competence with electricity, the acronyms and charge carriers could be problematic (the acronym question, I thought, was a nice question, but if you abandoned electricity I could see it being problematic).

Question six I thought was quite nice, but the resultant of two vectors experiment could easily be overlooked in revision, and the final part must have been difficult to anyone not doing applied maths.

Question seven was interesting in how it asked to calculate the energy of each photon rather than immediately going into the "n(wavelength) = dSin(a)", and even then it was interesting that they made you calculate the lines per millimetre rather than the more common 'maximum amount of orders visible'. The laser/vapour lamp part was an odd question too.

Question eight I didn't do, but operation of a heat exchanger thown in, the example of a moderator, and the final part seem like potential pitfalls.

Question nine, I have no idea as I absolutely hate electricity, but the difference between a battery and capacitor seems peculiar.

Question ten was an absolutely lovely question, but addition of the electricity component could have made it somewhat problematic for students who dislike electricity (I didn't personally have an issue with it, but I can definitely see how it would be problematic).

Question eleven, I didn't do, but the final two parts of the "a part" seem somewhat difficult (the expression one, however, seems like it could be found/worked out from the tables though, so maybe it's not too bad). The "b part" I didn't do, but depending upon how competent you are with light and waves, the fibre-optics part, and the critical angle of the glass part, coould have been annoying.

Question twelve was very nice, however. The "a part" was straight forward if you're competent with Simple Harmonic Motion (personally, I love it, and it's one of my favourite topics, but I know many others absolutely hate it), but it was annoying in the amount of decimals used and the very small measurements. The "b part" seems very fine, and the only real issue I can imagine is in the mathematics, and in confusing which shape of mirror is convex and which is concave. Overall though, it was very standard. The "c part" was mostly straight forward. I could see potential errors in the mathematics of calculating the temperature, in using one cube (which I ended up doing) instead of three, in taking the change in temperature rather than the temperature of the water (or a maths slip relating to this), and in deciphering whether it meant the instant the ice melted or if it meant when everything settled. The "d part" seemed very generous honestly, even if I avoided electricity like the plague where possible and ultimately didn't do it.

Overall, question six, question nine, question eleven "part a", and all of question twelve was fairly 'pure' in that they examined a single topic, but the others seemed to have some mixture of topics, and had some areas that could cause difficulty for students.

FatRat wrote: »

I didn't even do the mechanics question but I always though that to get max height all you need to do was find the height when the velocity = 0 ?

This is partly the case, but in the final part of question six there was both a horizontal and vertical component to the velocity. Therefore, the maximum height occurs (as you've said) when the vertical velocity is equal to zero (the magnitude of the ball's velocity doesn't equal to zero though because it still has an i-component). This allows you to get the time to reach the maximum height, and you can then substitute this into the vertical displacement formula. Splitting the velocity into its components is where the main difficulty may arise. For those that do applied maths, it's a very basic question, but I can see how it could be problematic if you don't.

Peregrine

FatRat wrote: »

I didn't even do the mechanics question but I always though that to get max height all you need to do was find the height when the velocity = 0 ?

Yes, but it was projected at an angle so you had to resolve the velocity into horizontal and vertical components, then find the height when Vy = 0.

FatRat

Solid_Shepard wrote: »

Question three was standard, except for that absolutely bizarre final part (which I certainly got wrong), where it was asking you to talk about graphing/getting the slope (as the y-intercept = -.03d) without actually asking about it directly that.

What's this? Are you sure that's the answer? For that part I took the difference in length between the first resonance and the second resonance. This is the same length as an anti-node to the next anti-node i.e. half a wavelength. Therefore multiply the length by two and you have your wavelength. Then use the formula c= f x lambda ??

aleatorio

FatRat wrote: »

What's this? Are you sure that's the answer? For that part I took the difference in length between the first resonance and the second resonance. This is the same length as an anti-node to the next anti-node i.e. half a wavelength. Therefore multiply the length by two and you have your wavelength. Then use the formula c= f x lambda ??

Yeah I remembered the l2-l1 part but couldnt remember the way to put it back in the formula so I just said c = 4f(l2-l1)
Close enough :pac:

Solid_Shepard

FatRat wrote: »

What's this? Are you sure that's the answer? For that part I took the difference in length between the first resonance and the second resonance. This is the same length as an anti-node to the next anti-node i.e. half a wavelength. Therefore multiply the length by two and you have your wavelength. Then use the formula c= f x lambda ??

I'm unsure that that is precisely what they're looking for, but it's what my teacher had said following the examination, and searching for the answer led me to this website mathsphysics.com/Physics/SpeedOfSound.htm which states "It is also possible to calculate an average value by graphing l (y-axis) against 1/f. Since l = (c/4)(1/f) - 0.3d the value of c is calculated by finding the slope (c/4) of the graph and multiplying it by 4." and that seems like a possible answer. Ultimately, I'm not sure what they're looking for, I just had assumed it was the graph, I hadn't even considered what you've just stated but it does sound like a logical way to work out the answer.

Flickka

I just realised that I only did 5 short questions in Q5 instead of 8. I just saw the do 5 questions in Section A at the top of the page and didn't think. Fml.

LCMATHS

I don't know why people found that paper so easy, the experiment questions were at best as easy as the previous years, but they all had hard parts in them making them slightly harder than previous years in my opinion. Question 5, my favorite question was extremely difficult, usually question 5 is simple, and if you go through the past question 5s you'll see the same stuff always comes up, I think that was one of the hardest question 5s so far. The particle physics question was different from previous years, and compared to last year was much harder in my opinion. I suppose the other questions were nothing out of the ordinary, but nothing about them was easy at the same time. I can understand people being happy with the paper, but to say it was suspiciously easy and that the marking scheme is going to be rough to compensate for the easiness is nonsense. Most people in my class found it very difficult in fact, harder than the mock even, and I agree, I don't understand what was easy?

mcratsix

I found the paper fine. The end of the experiment q's were weird, especially the q on how to find the speed of sound in air without measuring the diameter. I have a specific book on lc physics experiments and knew them all, but that's nowhere in the book, and that was annoying. I don't really get why everyones complaining about q5. Boyles law, rutherfords model, Cockcroft-Walton exp, rcd and mcb, they're all fairly basic IMO. The u-value thing was weird, but it was all in the log tables. Same with the mass of Mars, just use the formulae in the log tables. The thermometric properties is a fairly common q too. If you do app maths, q6 was amazingly simple. The nuclear q was tough to be fair. Q12 had something for everyone. Particle physics q was a little strange. Overall, I thought the paper was maybe 10% harder than average, at most.

If you don't do app maths, and I realise most people don't, and you had banked on an easy q5 and an easy q10, then I can see why you'd have been a bit thrown by the paper. Even so, I did qs that I'd normally never do, like the Wheatstone bridge thing and it was fine.

2thousand14

The Nuclear question was great for anyone doing engineering

Overheal

FatRat wrote: »

Anyone know if gravity was a correct force in the last part in q1? I said gravity and I levelled the air track to avoid the force.

Technically gravity is not the force, gravity is an acceleration. Weight is the force of mass accelerated by gravity, F=ma

FatRat

Overheal wrote: »

Technically gravity is not the force, gravity is an acceleration. Weight is the force of mass accelerated by gravity, F=ma

I said "the force of gravity" which is technically acceleration, yeah. But in the book it says everywhere that gravity is a force, as in 9.8 ms^-2 ...

2thousand14

Overheal wrote: »

Technically gravity is not the force, gravity is an acceleration. Weight is the force of mass accelerated by gravity, F=ma

Isn't gravity one of the fundamental forces of nature?

mcratsix

If you just said "gravity" they mightn't give you the full marks since gravity is an acceleration. If you said "the gravitational force" then you'd be fine.

Peregrine

2thousand14 wrote: »

Isn't gravity one of the fundamental forces of nature?

Gravitational force is. They won't give marks if you say gravity is a fundamental force of nature.

2013 Q6

(iv) Name the type of acceleration that the ISS experiences as it travels in a circular orbit around the earth.
centripetal / gravitational
What force provides this acceleration?
gravitational (do not accept “gravity”)

FatRat

Ok to clear this up.. in 2005 the principal of conservation of momentum came up. Last question was: "How were the effects of friction and gravity minimized in this experiment?". Answer was to adjust the slope of the track.

So that's cleared up. But nimrod is right, they wont accept "gravity" it has to be "force of gravity".

CianDowd

TheBegotten wrote: »

Anyone else think that last part of the particle physics question to be rather sneaky? And the Beta - decay, I don't even think that's on the course!

Beta decay is on the course but I have no idea what the last part was. I just went through the log table sticking in pieces of equations to do with what they asked for... :$ XD

CianDowd

MegGustaa wrote: »

I essentially did the same - S(y) = u(y)t - gt^2, differentiate to get V(y) and put it equal to zero to get time of max height, then sub that back in.
The angle was 15 degrees. I had u as 63.6.

I think that you're mostly right but in my answer I used:
S=ut+(1/2)at^2
So:
S(y)=u(y)t-(g/2)t^2
Whether you meant to type it I'm not sure but I think that g had to be halved.

EoghanIRL

CianDowd wrote: »

Beta decay is on the course but I have no idea what the last part was. I just went through the log table sticking in pieces of equations to do with what they asked for... :$ XD

All you had to do was let f=qvB equals to mv^2/r

Mv is equal to momentum right ? Mass times velocity .
Divide across by v
Mv= qBr

Did anyone else do something like this or am I completely wrong ? Hoping this is ok as I couldn't see a different way to do it.

Aspiring

EoghanIRL wrote: »

All you had to do was let f=qvB equals to mv^2/r

Mv is equal to momentum right ? Mass times velocity .
Divide across by v
Mv= qBr

Did anyone else do something like this or am I completely wrong ? Hoping this is ok as I couldn't see a different way to do it.

I just replaced the v with rw so I got F = qrwB , just took a guess at it cos they asked for r in the equation

Teachm

F=qvB. F= mv^2 over r


Mv^2/r = qvB

mv/r =qB

mv= qBr

Gabrielazap

Just wondering what graph yee all drew for SHM q 12?:):-)

MegGustaa

CianDowd wrote: »

I think that you're mostly right but in my answer I used:
S=ut+(1/2)at^2
So:
S(y)=u(y)t-(g/2)t^2
Whether you meant to type it I'm not sure but I think that g had to be halved.

Oh yeah sorry, I did halve it in the exam, just forgot when I was typing it out here!