Physics Aftermath

E92

I tried it with the moments being about the 0 cm mark of the metre stick, it was even more wrong than when I ignored the weight of the metre stick.

Then I tried it the the moments being about the 50.4 cm mark of the metre stick, and since its about there the weight of the metre stck can be ignored.

E92

carlowboy wrote:

Agreeing with you apart from Q6. I don't do Applied Maths (was crap at it as I didn't put any effort in). If you knew omega^2=k/m, it was the easiest question on the paper.

Oh I thought 6 was a lovely question, as I said it saved my ass yesterday, I found it easy, but it was strange to see something so like Applied Maths on it. We only spent about a day or 2 in Physics on SHM, we spent over month on it in Applied Maths.

SuZyQ!

i thought the paper was really challenging and there was a few little bits that threw me off but I think I did weel Im hopping for a good solid B please god

lemansky

If you learn physics out of the book it was a hard paper because you had to apply knowledge more than is usual in physics,so it appeared harder than other years.But if you understand physics it was handy.

eZe^

lemansky wrote:

If you learn physics out of the book it was a hard paper because you had to apply knowledge more than is usual in physics,so it appeared harder than other years.But if you understand physics it was handy.

It also caught students out who only studied particular sections, mar shampla the emission spectrum question in the doppler effect section.

JC 2K3

E92 wrote:

I dont really like Post Mortems too much, but does anyone know the answer to Q1 part ii) and iii), or more specifically, how they worked out the answer? I'm just curious as to what people did, cause mine didnt equal(you should get the same answer for both parts, shouldn't you), and I'd like to know where I went wrong.

I got a difference of about 1 between them and said it verified the laws of equilibrium within experimental error.

lemansky

eZe^ wrote:

It also caught students out who only studied particular sections, mar shampla the emission spectrum question in the doppler effect section.

Exactly.They like mixing their sections together,even if it is only in small things like the silicon as a semiconductor question thrown into a heap of questions that were at odds with that one.
I suppose its another lesson that has to be learned for next year's leaving.You can't afford to leave things out.

lemansky

JC 2K3 wrote:

I got a difference of about 1 between them and said it verified the laws of equilibrium within experimental error.

After numerous attempts they eventually worked out equal for me.I kept leaving things out or hitting the wrong buttons on the calculator.Did you run the figures a few times and get one as the difference each time?

adam_ccfc

The clockwise and anticlockwise moments were exactly equal, as were the upward and downward forces.

Thomas_S_Hunterson

lemansky wrote:

After numerous attempts they eventually worked out equal for me.I kept leaving things out or hitting the wrong buttons on the calculator.Did you run the figures a few times and get one as the difference each time?

They worked out exactly equal for me too.

JC 2K3

Nah, I did it once and noticed I was running out of time.

I doubt a miscalculation warrants more than one lost mark though tbh.

I reckon I might have taken 50 as the mid point when working out the distance of one or two forces or something.

ZorbaTehZ

adam_ccfc wrote:

The clockwise and anticlockwise moments were exactly equal, as were the upward and downward forces.

Same for me.

lemansky

JC 2K3 wrote:

Nah, I did it once and noticed I was running out of time.

I doubt a miscalculation warrants more than one lost mark though tbh.

I reckon I might have taken 50 as the mid point when working out the distance of one or two forces or something.

Exactly.Its only a miscalculation not a case of not knowing what to do.Easy mistake to make as well.Thats what I did one of the times.

ZorbaTehZ

JC 2K3 wrote:

I got a difference of about 1 between them and said it verified the laws of equilibrium within experimental error.

1 Newton ... thats quite a big difference tbh.

JC 2K3

1 Newton centimetre

ZorbaTehZ

JC 2K3 wrote:

1 Newton centimetre

Iirc my answers went to two places of decimal, and still matched up number for number ... so even 1 Ncm is a lot tbh ... usually when it's diliberately not equal its usually, by 0.01 or something.

JC 2K3

Well if it was N m, the SI units, it would have been 0.01.....

But meh, not worth discussing really. I've lost one or two marks tops.

adam_ccfc

Just a quicky, in the Hooke's Law question, when it asked you to derive an equation that relates the acceleration to the displacement, I assume they just wanted you to turn F=-ks into a=(-w^2)(s) ?

Nehpets

adam_ccfc wrote:

Just a quicky, in the Hooke's Law question, when it asked you to derive an equation that relates the acceleration to the displacement, I assume they just wanted you to turn F=-ks into a=(-w^2)(s) ?

Yep, I think so. That's what I did

cocoa

adam_ccfc wrote:

Just a quicky, in the Hooke's Law question, when it asked you to derive an equation that relates the acceleration to the displacement, I assume they just wanted you to turn F=-ks into a=(-w^2)(s) ?

*shrug* they might have meant that, I assumed they meant adding the forces (gravity down, the elasticity up) and it kindah cancles out so that you're left with - a number by s.

Roonels

lemansky wrote:

If you learn physics out of the book it was a hard paper because you had to apply knowledge more than is usual in physics,so it appeared harder than other years.But if you understand physics it was handy.

well said i agree wholeheartedly. the previous few years have enabled you to spit answers onto the page, this year it turned out to be a bit different due to thought aspect.

adam_ccfc

cocoa wrote:

*shrug* they might have meant that, I assumed they meant adding the forces (gravity down, the elasticity up) and it kindah cancles out so that you're left with - a number by s.

I did that, but then I thought about it and crossed it out. Poorly worded, I thought.