[Oromis263]

(Original post by Amy-Rose)
Wondered if any light could be shed on these two ideas?

For the first one, you would use a large mass as to give the system a large inertia (ie, resistance to changes in it's state of motion) so that when an earthquake strikes, the ball doesn't move much at all, and it remains stationary (or near to). Then you have a stationary point from which you can measure the relative shaking of the ground from.

The other one is just the standard insert a constant, k, into the proportionality, then see if the value of k remains constant. Or you could plot a graph of E against A^1.5, and if it's a straight line, they are directly proportional. These type of questions have appeared in a fair few past papers, so you ought to be comfortable with them.

[Amy-Rose]

(Original post by Oromis263)
For the first one, you would use a large mass as to give the system a large inertia (ie, resistance to changes in it's state of motion) so that when an earthquake strikes, the ball doesn't move much at all, and it remains stationary (or near to). Then you have a stationary point from which you can measure the relative shaking of the ground from.

The other one is just the standard insert a constant, k, into the proportionality, then see if the value of k remains constant. Or you could plot a graph of E against A^1.5, and if it's a straight line, they are directly proportional. These type of questions have appeared in a fair few past papers, so you ought to be comfortable with them.

Also thank you to Dhanu123 for replying. That makes sense, I think I was possibly trying to overthink it. Following on the idea earlier in the article that it is difficult to have a mass suspended in the air staying still while the ground below is shaking?

EDIT: Looking now I can't see where I've mentioned this from, but anyway, thank you for clearing it up hehe!

Yes, you're right, I have seen similar on a few papers! So as long as you say either of those answers you will be correct? Alternatively lnE plotted against lnA should give a straight line with dy/dx at 3/2?

[Oromis263]

(Original post by Amy-Rose)
Also thank you to Dhanu123 for replying. That makes sense, I think I was possibly trying to overthink it. Following on the idea earlier in the article that it is difficult to have a mass suspended in the air staying still while the ground below is shaking?

EDIT: Looking now I can't see where I've mentioned this from, but anyway, thank you for clearing it up hehe!

Yes, you're right, I have seen similar on a few papers! So as long as you say either of those answers you will be correct? Alternatively lnE plotted against lnA should give a straight line with dy/dx at 3/2?

Yes, that graph would be suitable, if a little bit of effort!

[Amy-Rose]

(Original post by Oromis263)
Yes, that graph would be suitable, if a little bit of effort!

Yeah you're right.. all right in those questions asking you just to describe the steps mind you.

Are people doing Section C first or leaving it til last?

[Oromis263]

(Original post by Amy-Rose)
Yeah you're right.. all right in those questions asking you just to describe the steps mind you.

Are people doing Section C first or leaving it til last?

I tend to try blitz Section A, get all that out of the way, then read through Section B, attempt all the easy looking number stuff, leaving the wordy bits for when I've decided how best to write it, and from there I just back and forth between questions in Section B and Section C. Often, if I know an explanation for a Section C bit I'll try get that down quickly.

[In One Ear]

(Original post by Oromis263)
I tend to try blitz Section A, get all that out of the way, then read through Section B, attempt all the easy looking number stuff, leaving the wordy bits for when I've decided how best to write it, and from there I just back and forth between questions in Section B and Section C. Often, if I know an explanation for a Section C bit I'll try get that down quickly.

I find this sort of jumping around takes far too much time and breaks my "flow" if you will. I prefer just to go through in order ticking the questions off 1 by 1 so i know exactly what my progress is like. Of course this assumes a paper than i find reasonably do-able. If its a really hard paper then as soon as i realise i'm unlikely to be able to do a question/part of a question, i cut my losses and move on doing all that i can until i reach the end then use whatever time i have left to have another go at the parts of questions i missed out. I'd be too worried about forgetting to do parts of questions to do it your way!

[littlemissmidget123]

Please can someone help me!

Explain what effect that the wave velocity increasing would have on the left hand section of the diagram in box 1?

What would this do to theta 1 and theta 2?

[In One Ear]

(Original post by littlemissmidget123)
Please can someone help me!

Explain what effect that the wave velocity increasing would have on the left hand section of the diagram in box 1?

What would this do to theta 1 and theta 2?

V2>V1 means LHS<1 means sintheta2>sintheta1 means theta2>theta1.

[littlemissmidget123]

(Original post by In One Ear)
V2>V1 means LHS<1 means sintheta2>sintheta1 means theta2>theta1.

I understand that.... but youve basically just stated v1/v2 = sin theta 1/sin theta 2

i want to know what the change of velocity actually does to the angles i.e. do they get bigger or smaller?

[Dhanu123]

Depends on the medium being entered I'm guessing.

and in one of the model questions, there's a question where they give you a picture of chang heng, and they want you to discuss it... would something like that ever come up?
if so, what sort of answer are they looking for?

[Oromis263]

(Original post by Dhanu123)
Depends on the medium I'm guessing.

and in one of the model questions, there's a question where they give you a picture of chang heng, and they want you to discuss it... would something like that ever come up?
if so, what sort of answer are they looking for?

No, I believe that was a witty physics teacher who added that in as a joke. ¬¬ :P Confused me at first too.

[In One Ear]

(Original post by littlemissmidget123)
I understand that....but youve basically just stated v1/v2 = sin theta 1/sin theta 2

No i havn't, i used snells law to deduce how the two angles are related.

i want to know what the change of velocity actually does to the angles i.e. do they get bigger or smaller?

I told you, if you know the velocity in the second medium is greater, then you know theta2>theta1, i.e., the wave bends away form the normal.

Explain what effect that the wave velocity increasing would have on the left hand section of the diagram in box 1?

This question is confused and doesn't make sense. The LHS of the diagram gives the entry angle (measured from the normal to the new medium being entered) and the entry speed. These are what these are. If you increase the incoming velocity, then the ratio of the angles still remains the same, just the bent wave in the second medium is also going faster than before.

What i think you meant to ask, is what happens to the second angle relative to the first in the case that (1) the wave travels faster in the second medium; (theta 2 >theta1 as i showed above) and (2) the wave travels slower in the second medium; (theta 1>theta 2).

[littlemissmidget123]

Another question I'm stuck on..

Question 5d from the third set of questions - derive an equation..

Is it just

time = 2 x root (1/2 x^2 + k^2) / v

??


EDIT - so what would the graphs for 5b and 5d look like - should they be the same - but with a longer time and distance travelled if you gave t and x figures?

sorry for the questions.. this bit is just getting me confused!!

[Dhanu123]

hmmm, i sure the only equation you need for 5 is

T= 2Pi * Root(L / g)

[littlemissmidget123]

(Original post by Dhanu123)
hmmm, i sure the only equation you need for 5 is

T= 2Pi * Root(L / g)

but that has nothing to do with the question - which is to derive an equation for time, t in terms of x k and v

[Dhanu123]

(Original post by littlemissmidget123)
but that has nothing to do with the question - which is to derive an equation for time, t in terms of x k and v

oops, sorry i was looking at the wrong set of questions

EDIT. sorry, im with you now. yeh i got

T = (2 * Root(0.5x^2 + k^2))/v
it's just Pythagoras x 2

[sarah-madeline]

may seem like a really stupid question right, but when you do SHM
(or snells law) do you work in degrees or radians?

[silvertear]

Does anyone know if there is a answer document for the 3rd set of pre-release questions by Bradfield College?

[Amy-Rose]

Hahahah, on the mention of that Chang Heng question, I found it quite entertaining. Reminded me of that parody of that AQA Biology exam from a few years ago!

Think I may do Section C last, follow it in the order as I go along. :P

[littlemissmidget123]

(Original post by silvertear)
Does anyone know if there is a answer document for the 3rd set of pre-release questions by Bradfield College?

not that i'm aware of.. however im now stuck on question 6b and c too... god i wish there was an answer set!