Physics Discussions

Mutant_Fruit · 20-06-2004 10:33pm

Originally posted by The Shol'va
The Chief said the article question could be on Microwaves and Telecommunication

What kind of stuff has to be looked over to answer a question on that.

Apparently the electricity circuit in the house is tipped for question 11.

What can they possibly ask you on that?

subway_ie · 21-06-2004 8:04am

Originally posted by Smellyirishman
I bet you get a B or C subway, me on the other hand, im actually screwed! Looking for a D and then ill be as happy as a pig in things that make him happy

Right now, a B1 would be gorgeous. But at best I'll get a C2/C1. I *need* a B1 at least in this, so that's why I say I'm fairly screwed.

Mutant_Fruit · 21-06-2004 8:07am

Originally posted by penguincakes
"What is physics?"

I remember the first thing we did in physics class was answer that very question. We answered one by one, and practically half the suggestions of the class were dismissed as being "Mechanics", which was mentioned by the first chap.

NeoSlicerZ · 21-06-2004 12:57pm

Beaut of a paper.

Smellyirishman · 21-06-2004 1:16pm

Twas great!!!

Definitly got my D (Lmao a t a D!) perhaps got a C, but definitly got my D!!

Great paper! I did Q1,2,3,4 5,9,10,11,12

Messed up here and there (called the live wire Red

)but it was a great paper!

That has relieved so much stress from me its unreal!! This test was the make or break test and I pwned it!! (lol didnt own it but I did OK considering what I was expecting!)

PrecariousNuts · 21-06-2004 1:28pm

Wow, what a paper. It was perfect, nothing hard/complicated at all. I actually managed to get every single question on the paper done, yep all 12. Come on A1!

BangBeater · 21-06-2004 1:36pm

Just wondering what other ppl's answers were for the last part of Q6

(i) Velocity of bob?
(ii) Velocity of block?

Average force?

subway_ie · 21-06-2004 1:38pm

Lovely paper, although I doubt I'll get higher than a B1. And, for once, the predictions were actually true (for the most part anyway). If only applied maths is like that too...

subway_ie · 21-06-2004 1:42pm

I don't have the answers to the bob and the block - but all I did was get the mgh (potential energy) and let that equal to .5mv^2 (kinetic energy) and then solve for v. I used m1u1 + m2u2 = m1v1 + m2v2 in there somewhere too. For the average force, I got 0.1224N, but I think I fecked that up somehow. And I'm supposed to be able to do applied maths :rolleyes: .

subway_ie · 21-06-2004 1:44pm

Originally posted by Mutant_Fruit
What can they possibly ask you on that?

Well, stuff about fuses, RCDs, MCBs, voltage-time graphs, wiring in a plug, storage heaters, all that kind of thing...

I was surprised that doppler wasn't anywhere on the paper though. It did seem to resemble the 2002 sample paper alot.

PrecariousNuts · 21-06-2004 1:46pm

No I got the same answer as you subway, it seems right

(i) was 1.7 something I think
(ii) 2.45 ish

Could be completely wrong since I'm just guessing

subway_ie · 21-06-2004 1:55pm

Originally posted by PrecariousNuts
No I got the same answer as you subway

Hmmm. That could be a very, very bad sign.

SeanPuddin · 21-06-2004 1:56pm

bob was 1.98 m/s

block went at 12.25 m/s

average force 0.3N

i hope!
can't figure out where i went wrong....

subway_ie · 21-06-2004 1:59pm

SeanPuddin - what method did you use? For the average force, I just stuck in F=ma and hoped for the best. My method for (i) and (ii) is above.

SeanPuddin · 21-06-2004 2:01pm

i) potential energy = kinetic energy

v = 1.98

ii) Prinicipal C of Momentum

remember that block weighs absolutely natin!

v = 12.25

iii) v^2 = u^2 + 2as

got a

use F=ma

F=0.3N

PrecariousNuts · 21-06-2004 2:01pm

mgh = 1/2 mv^2
2gh = v^2
v^2 = 3.92
v = 1.97 ms-1

m1v1 = m2v2
10(1.97) = 8v2
v2 = 2.47 ms-1

v^2 = u^2 + 2as
0 = (2.47)^2 + 4a
6.125 = -4a
a = -1.53 ms-2

F = ma
F = 0.01225N

PrecariousNuts · 21-06-2004 2:02pm

remember that block weighs absolutely natin!

what

subway_ie · 21-06-2004 2:03pm

Originally posted by SeanPuddin
remember that block weighs absolutely natin!

Actually, it weighs 0.008KG...

Swifty · 21-06-2004 2:05pm

Easier than I expected! Fairly happy with that. I am now finished this leaving cert bull****.. Goodbye!

SeanPuddin · 21-06-2004 2:06pm

you didn't convert your masses to kg!

subway_ie · 21-06-2004 2:07pm

Originally posted by SeanPuddin
you didn't convert your masses to kg!

It doesn't really matter - they just cancel anyway (the decimal points that is).

PrecariousNuts · 21-06-2004 2:07pm

I didn't need to, you might notice that I used grams on both sides, converting to kg would have been like dividing both sides by 1000.

SeanPuddin · 21-06-2004 2:08pm

it does matter it comes to 24.625 that way. I think i got that question wrong, but you have to convert defo.

PrecariousNuts · 21-06-2004 2:10pm

only for the F = ma bit, don't argue with applied mathematicians

subway_ie · 21-06-2004 2:11pm

Originally posted by SeanPuddin
it does matter it comes to 24.625 that way. I think i got that question wrong, but you have to convert defo.

No. You don't have to convert defo. You can if you want, but it's just more work. Look at precariousNuts workings and try and see where he went wrong... he didn't. Like he said, converting is just like dividing both sides by 1000. You can if you want, but there's no need. Just like you could divide both sides by 12464321514216 if you wanted to, and it would still be true. But why would you?

SeanPuddin · 21-06-2004 2:11pm

i do app. maths....maybe i shud be quiet now! :rolleyes:

PrecariousNuts · 21-06-2004 2:12pm

m1v1 = m2v2
10(1.97) = 8v2
v2 = 2.47 ms-1

as opposed to

(.01)(1.97) = (0.008)v2
v2 = 2.47 ms-1

PrecariousNuts · 21-06-2004 2:15pm

hohoho

subway_ie · 21-06-2004 2:28pm

I did:

Section A:
Q.1 - Lovely quesiton, although I did make a stupid mistake with the graph (read the word "suitable" and for some reason instead of taking the obvious l against t^2 route, I did a velocity-time graph... only copped on with about 10 mins to go and did it over again - although the values I got using my velocity-time graph gave me a g-value of 9.86m.s^-2, as opposed to 10.309 with the right graph)
Q.3 - Amazingly easy question. So short for a section A too. They even gave the graph, you'd have been mad not to do this question.
Q.4 - Again, a lovely question - the only part I didn't do so well in is describing how to use the micrometer... just waffled on a bit. I got 1.41x10^-6§Ùm for the resistivity, dunno if it's right.
Q.5 - All easy... but I got stuck on (b) and (d) - I got 980N for (b) and 20 times for (d), both of which are probably wrong.
Q.6 - Totally forgot the proof of F=ma, so I just wrote about momentum proportional to force and wrote down F=ma a few times. Might get a few marks for it.
Q.7 - Somehow I managed to mess up my formula for these ones. I got 112.5kJ for part (i) and 1406.25s for part (iii).
Q.8 - Should have done this question, didn't have time.
Q.9 - For the calculation of the threshold frequency I used c=f¥ë, again, probably wrong. Then I used E = hf + .5mv^2 for the second part. Don't know where I got that from...
Q.11 - I said a 13 amp fuse for (c) - total guess. And the voltage-time graph, I just did a sine wave...
Q.12 (a) and (d) - didn't know how to explain the good conductor after 0.6v bit.

If anybody can be bothered to read all of that, then feel free to improve on my answers (can't be that hard really).

subway_ie · 21-06-2004 2:31pm

Originally posted by PrecariousNuts
hohoho

Your shameless endorsement of McDonalds has finally ended!

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