Physics !!!! (H)

sixdraw

thinking about it i don't know if that makes sense but i remember my teacher going on about that

sixdraw

oh yeaaaah, its in the real world book.for a given power if the voltage is large the current is less. p = iv. and with p=i^2R less energy loss

upmeath

Yeah I'm pretty sure I made some sort of reference to Joule's Law in there too... I tend to write short essays for those sort of questions, once the right words are in there the marks are yours with a lot of physics. It's almost like "refer to the text" in English!

Webmonkey

Richard_Fonzie wrote:

hmmm, that's not what I did. I used Ep = mgh, where Ep is the energy needed to bring the ball to a height h. Kinetic energy was 17.934 when it reached the ground, but it lost 6, so then it had 11.934 on the way up:
(11.934)=(.6)(9.8)h
h=2.03m


That was the same number as I had, except the power was ^-9 .

To be honest, i thought the Q.11s were sweet. Just about everything they wanted you to say was indicated in each question. Better than having 18 mark questions that simply translate as "write all you know about". Instead the types of questions today helped you associate questions to information.

Hmm im getting confused now.

Ok Kenetic energy at ground =~ 17joules. It said it lost 6 Joules so potential energy gained = kenetic energy lost. Thus is it 6 joules gained so it had 6 joules of energy.
God i hope yer wrong, i don't wanna see these kind of mistakes. Someone else confirm that Q12 a was 1.02 meters or 2meters?

rasher_b2

Webmonkey wrote:

Hmm im getting confused now.

Ok Kenetic energy at ground =~ 17joules. It said it lost 6 Joules so potential energy gained = kenetic energy lost. Thus is it 6 joules gained so it had 6 joules of energy.
God i hope yer wrong, i don't wanna see these kind of mistakes. Someone else confirm that Q12 a was 1.02 meters or 2meters?

I think I got the 2meter answer too.

sixdraw

the 6 J is lost. ie converted to heat or sound not potential. the remaining kinetic energy is the potential gained.
Funny thing is, i found the question confusing so i did it both ways

Webmonkey

Damn. Ah its ok i got another question to replace it anyways. I think i miss read the question. I don't have the paper, could someone tell me what the exact question was. I know i'm wrong alright id say

Richard_Fonzie

If you wrote down Ep=mgh you'll get quite some marks.

Señor Juárez

http://www.examinations.ie/archive/exampapers/2005/LC021ALP1EV.pdf

The Failed God

sixdraw wrote:

the 6 J is lost.

If you mention the phrase that energy is lost they'll murder you,doubt you'd get mark "energy cannot be created or destroyed but can be converted from one form to another"

whenthepawn

sixdraw wrote:

the remaining kinetic energy is the potential gained.

the remaining energy ( ie 11 J) is the kinetic energy to be used in going the next bounce, isnt it ?

i said 11= 1/2 mv^2 worked out v and used uvats equations to get s.
i got something like 2.02

*Angel*

whenthepawn wrote:

the remaining energy ( ie 11 J) is the kinetic energy to be used in going the next bounce, isnt it ?

i said 11= 1/2 mv^2 worked out v and used uvats equations to get s.
i got something like 2.02

Yeah that's what I did, I found v^2, which would be u^2 in the equation, v^2 = u^2 + 2as, where v = 0, a = g.

exiztone

M = 0.6KG
g = 9.8
H = 3.05

Maximum kinetic energy = MgH = 17.934

The 6 joules was converted to other forms like sound or heat

First bounce, the potential energy is 17.934 - 6 = 11.934

Then you do: 11.934 = (0.6)(9.8)H

H = 2metres

It makes sense if think about it, I mean, the first bounce of a basketball will be high, but it's not going to be as high as where it was dropped from.

Moira

dont know did i get those answers but got 3 something metres for the bounce, dunno why ye are using e=mgh when its kenetic energy as the ball is falling, i used the equations of motion as well as far as i rememeber v^2=u^ + 2as, then for the bounce bit i took acceleration as minus g and got 3. somthing? the only part that u talk about potential energy is that once it bounces the ground gains potential, dont tell me u had to work that out too??

Alkers

3m something has to be wrong. It was only dropped from 3m in the 1st place. I got 2.02m, the same as most people I know. Worked out v2 for when the ball hits the ground. This was U for the first bounce then used the acceleration formulae - came out in 2odd minutes, very nice question.

Webmonkey

Moira wrote:

dont know did i get those answers but got 3 something metres for the bounce, dunno why ye are using e=mgh when its kenetic energy as the ball is falling, i used the equations of motion as well as far as i rememeber v^2=u^ + 2as, then for the bounce bit i took acceleration as minus g and got 3. somthing? the only part that u talk about potential energy is that once it bounces the ground gains potential, dont tell me u had to work that out too??

Well Kenetic and Potential Energy have a huge relationship.

When something speeds up it gains kenetic and loses potential proportially, and vica versa.
Yeah guys your right i just took it as being it lost 6 joules going up so what height was it at that instant. Damn it

So yes it had a max of 11Joules from the begining, as it rises it loses this 11 joules so at Max Height it has max potential and min kenetic. So 11Joules is with the potential thus is why we use the formula Ep = mgh.
3 m is definetely wrong unfortuntally. A lot of people use the motion formulas but the energy was so much easier at this time.

So yep 2.02m is the answer. I will lose around 3 - 6 marks i spose, still hope i've the A1.

Moira

from what i rememeber i got 3.02 but that could well have been 2.02 cos i seem to have done it the way people with that answer. actually i just did it all again and i think i went wrong at the end, got the same energy answers like the 17 and 11 but just dunno where i went then, i think i might have gone backwards for some strange reason?? i do have a habit of doin weird things when it comes to calculations.

sixdraw

The Failed God wrote:

If you mention the phrase that energy is lost they'll murder you,doubt you'd get mark "energy cannot be created or destroyed but can be converted from one form to another"

i was quoting the paper , "on bouncing from the ground the ball loses 6 joules of energy"
and of course i didnt give that on my exam, its converted to heat and sound

sixdraw

could that question not also be read, the ball loses 6 joules of kinetic energy on bouncing from the ground so energy goes to potential. thats why i gave both to cover my ass

Moira

i dont see anything wrong with that, like all i said was that if 6j is lost on bouncing it is converted into other forms of energy such as heat and sound and the ground gains potential energy or something along those lines. id say u covered ur ass alright.

OTliddy

omg so many posts about one sum!...I got 2.02m
for question 4(ii) when they say "from the graph", do you just say 1V=27.5mA and 5V=92.5mA then use V=IR?

Webmonkey

it was easy to miss interperate (wrong spelling?) the question. I did. I thought it ment from the bouncin stage it lost 6 joules meaning the potential gained was 6. Ahhhh doesn't matter only few marks anyways. Yep way 2 many posts on this sum!

Webmonkey

ok i just looked at the question now and yes the 2.02 is prob the one alright. I think i even missed the 4 mark one, i took it all as being on question. oh well

exiztone

In 12 part C, there's a 6 point question that asks for two other factors that affect the frequency of a string.

I said:
Tension
Mass per unit area <-- This is supposed to be Mass per unit length

How many marks do you think I'll get out of the 6?

Moira

6 mark q is usually divided 3+3 so id say 3 just for the tension, mass per unit length isnt one of the experiments anyway and i always thought that it was tension and length that affected it? i didnt do the q myself and wouldnt be relaly strong at the waves so could well be wrong, hope i am and u get ur 3 marks, it can be the difference of a grade like!

sixdraw

no its proportional to mass per unit length and i think you might get 1 or 2 marks for the "mass per" part. don't be thinking about little bits like that, its allready done
f ~ 1/(root mass per unit length)

I know I've left it a bit late, but anyway......


Question 1:
Out of all the trolley questions, this was the only one I didn't think would come up. Although I did do very well in it, perhaps full marks (although I am a very bad drawer).

Question 3:
The highly predicted question. Full marks. Got 1.45 for the refractive index.

Question 4:
Once again, very easy and very predictable. I even remebered to put a milli-ammeter instead of an ammeter in the circuit diagram. Hopefully I got full marks.

Question 5:
Answered all ten. VERY easy.

Question 6:
Another predicted question. The only thing I may have dropped marks was that I actually EXPLAINED the Doppler Effect, but never stated that it WAS the Doppler Effect. Hopefully I'll still get all the marks. If I remeber correctly I got 66 2/3 minutes for one of the answers.

Question 9:
Very nice question. Got 600 ohms and 4mA I think. Hopefully all the marks again.

Question 11 (a):
As people have been saying, it was EXTREMELY easy. Full marks for sure.

Question 12 (b):
A nice question. Simple and straightforward.

Question 12 (d):
Einstein's 100th anniversary thing came up, so I was really happy!


Overall, I'd expect 98%-100%. The only thing I could have lost marks in was that I didn't state the Doppler Effect and that I'm a crappy drawer. I'm very pleased with my result, especially after my dismal Maths exam, and I'll be walking into my App. Maths exam full of confidence.

*Angel*

Why does everyone here seem to hate the experiment to find the specific latent heat of vaporisation of steam? I think only one other person said they did the experiment. It's easy stuff and the question was easy and predictable.

Webmonkey

I done it. It was a dos of a question. Forumla looks scary but it makes sense in the end of the day and could be made up yourself if you think bout it.

Did you get an answer of 215742Joules or something liek that. It started with 21 anyways i think

*Angel*

Webmonkey wrote:

I done it. It was a dos of a question. Forumla looks scary but it makes sense in the end of the day and could be made up yourself if you think bout it.

Did you get an answer of 215742Joules or something liek that. It started with 21 anyways i think

Yep, I can't remember the exact number but sounds right.