Physics Discussions

doppler and big section don't go well together

Originally posted by Mutant_Fruit
well, just finished reading my ENTIRE physics book.

You read all of Real World Physics? And you're still conscious??? 'Tis quite a feat. I'm sticking to my Dan O'Regan revision book... clear, concise and less mistakes.

read the whole book, and i'm planning on reading some of the more important definations/sections/experiments again tonight, and again tomorrow morning.

Obviously i didn't read every single word though i read the important parts like definations/experiments, and stuff i didn't know. Stuff i definately knew (like linear motion) i skipped completely.

EDIT: i wrote night instead of morning

I've gotten grinds off an examiner for Physics (I'm still no physics genuis mind you) but he's given me a better idea of what they want. Apparently some of the explanations of things you see in Real World Physics aren't exactly what they want from you. For example the lightning conductor explanation is fairly small compared to the one this guy gave me.

For some of those "use your graph to estimate" questions you need to manipulate the formula a fair bit to derive a new equation involving the slope, none of which are in the book.. I've seen these mainly in the "stretched string" sound practicals.

Particle Physics 100% definate then? That's good. Hopefuly they wont come out with dodgy calculation questions.

He never gave any predictions, doubt he has anything to do with setting the paper, he just corrects them. Sorry!

Emf = electro-motive force = the force which occurs when electrons move through a body.

Dunno bout the ampere, it's some long crap one. I'm not doing the big electricity qs so...

I'm so fecked. This is the only exam that I feel totally unprepared for. At least going into the others I was under the illusion that I was prepared, but this one I know I'm not ready for it. 12 hours 15 minutes to go.

Im looking at

wavelength
Pendulum
String
..something

For section A

And section B I havent got a clue, just whatever comes up ill give it a bash!

Have a look at some mechanics people. That's my final advice before bed.

The Chief said the article question could be on Microwaves and Telecommunication, and the Cheif ain't wrong :P

And Mechanics is INCREDIBLY easy if you do applied maths

Now... time to start studying... over 11 hours of time :P

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?

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.

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!)

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: .

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

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....

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

remember that block weighs absolutely natin!

what

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

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).

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

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?

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

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).